Using concentrations of solutions in mol/dm3

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Concentration in mol/dm³

Concentration can be measured in mol/dm³ (also written as mol/dm³ or mol/dm³).
It is often more useful to express concentration in moles per unit volume rather than mass per unit volume.
The formula is: concentration (mol/dm³) = number of moles of solute (mol) ÷ volume of solution (dm³).
The units in the answer can be written as mol dm⁻³ or mol / dm³.
You may need to convert between g/dm³ and mol/dm³ depending on the question.

Concentration, moles and volume formula triangle

Converting between cm³ and dm³

To go from cm³ to dm³, divide by 1000.
To go from dm³ to cm³, multiply by 1000.
For example, 500 cm³ ÷ 1000 = 0.5 dm³.
A common mistake is forgetting to convert units, which gives an answer a thousand times out.

Calculating moles from concentration and volume

Rearrange the formula to find moles: moles = concentration × volume.
Make sure the volume is in dm³ before substituting into the equation.
A formula triangle can help you rearrange the relationship between concentration, moles and volume.
You are not given the formula triangle in exams, so you must learn it.
It is a good idea to write the formula down before starting a problem.

Worked example: moles from concentration

Calculate the moles in 2.5 dm³ of a solution of concentration 0.2 mol/dm³.
Moles = concentration × volume = 0.2 × 2.5.
The answer is 0.5 mol.

Worked example: concentration from mass

Calculate the concentration of sodium hydroxide, NaOH, when 80 g is dissolved in 500 cm³ of water (Na = 23, H = 1, O = 16).
First find the relative formula mass: Mᵣ(NaOH) = 23 + 16 + 1 = 40.
So 40 g NaOH = 1 mole, and 80 g NaOH = 2 moles.
Convert volume: 500 cm³ ÷ 1000 = 0.5 dm³.
Concentration = moles ÷ volume = 2 ÷ 0.5 = 4 mol/dm³.

Titration calculations

If the concentration of one reactant is known, the exact volumes from a titration and the balanced equation can be used to find the concentration of the other reactant.
Use the equation for the reaction to find the mole ratio between the acid and the base.
Calculate moles of the known solution using moles = (volume ÷ 1000) × concentration.
Use the mole ratio to deduce the moles of the unknown solution.
Finally, calculate concentration using concentration = moles ÷ volume (dm³).

Worked example: titration calculation

25.0 cm³ of hydrochloric acid was titrated against 0.100 mol/dm³ NaOH; 12.1 cm³ of NaOH was required.
Equation: HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l).
Moles of NaOH = 0.012 dm³ × 0.100 mol/dm³ = 1.21 × 10⁻³ mol.
The acid reacts in a 1:1 ratio, so moles of HCl = 1.21 × 10⁻³ mol.
This is present in 25.0 cm³ = 0.025 dm³.
Concentration of HCl = 1.21 × 10⁻³ ÷ 0.025 = 0.0484 mol/dm³.

Key terminology and practical skills

Titration is used to determine the concentration of a strong acid or alkali.
A pipette is used to measure a precise volume of one solution into a conical flask.
A burette is used to add the other solution until the end-point is reached.
A standard solution is one whose concentration is accurately known.
Concordant results are titres within a small range (e.g. 0.10 cm³) of each other; only these should be averaged.
Neutralisation occurs when an acid and alkali react completely.

Common misconceptions and errors

Failing to convert cm³ to dm³ gives answers a thousand times out.
Do not confuse g/dm³ with mol/dm³ — they are different units.
Do not average non-concordant titres; only use concordant results.
A more concentrated solution is not necessarily a stronger acid.
When reading a burette, read from the correct end of the scale (top to bottom).

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1.Which equation correctly gives concentration in mol/dm³?
Easy
- Aconcentration = moles of solute ÷ volume of solution in dm³
- Bconcentration = volume of solution in dm³ ÷ moles of solute
- Cconcentration = moles of solute × volume of solution in dm³
- Dconcentration = moles of solute ÷ volume of solution in cm³
2.A solution of sulfuric acid, H₂SO₄, contains 9.8 g of the acid in 250 cm³ of solution. What is the concentration in mol/dm³? (Ar: H = 1, S = 32, O = 16)
Medium
- A0.10 mol/dm³
- B0.20 mol/dm³
- C0.40 mol/dm³
- D0.80 mol/dm³
3.Which of the following statements about concentration and titration are correct? (select all that apply)
Medium
- AConcentration can be expressed in mol/dm³ or in g/dm³.
- BA more concentrated acid is always a stronger acid.
- CConcordant titres are within 0.10 cm³ of each other.
- DA burette is read from the top of the scale downwards.
- EThe pipette is used to deliver the solution of unknown concentration into the conical flask.
4.The concentration of a solution in mol/dm³ is the number of moles of solute dissolved in 1 dm³ of solution.
Easy
True or false?
5.Match each piece of titration apparatus or term with its correct description.
Medium
- pipette
- burette
- conical flask
- concordant results
- delivers a fixed volume of solution accurately
- delivers variable volumes and is read from the bottom of the meniscus
- used to hold the solution during titration and swirled
- titres that are within 0.10 cm³ of each other
6.Place the steps of a titration in the correct order.
Medium
- Pipette a known volume of the solution into a conical flask.
- Add a few drops of indicator to the conical flask.
- Fill the burette with the other solution and record the initial reading.
- Add the solution from the burette until the indicator changes colour.
- Record the final burette reading and repeat until concordant results are obtained.
7.How many moles of solute are present in 2 dm³ of a 0.5 mol/dm³ solution of potassium iodide?
Medium
- A0.5 mol
- B1.0 mol
- C2.0 mol
- D10 mol
8.In a titration, 25.00 cm³ of 0.20 mol/dm³ sodium hydroxide reacted with 26.50 cm³ of hydrochloric acid. What is the concentration of the acid? (HCl + NaOH → NaCl + H₂O)
Medium
- A0.19 mol/dm³
- B0.23 mol/dm³
- C0.55 mol/dm³
- D0.82 mol/dm³

Thêm câu hỏi

9.A student titrated 25.00 cm³ of 0.40 mol/dm³ sodium hydroxide with hydrochloric acid. The equation is HCl + NaOH → NaCl + H₂O. 20.00 cm³ of acid was needed. What is the concentration of the acid?
Medium
- A0.32 mol/dm³
- B0.50 mol/dm³
- C0.80 mol/dm³
- D1.25 mol/dm³
10.Which of the following are correct ways to express the concentration of a solution? (select all that apply)
Medium
- Amol/dm³
- Bg/dm³
- Cmol/cm³
- Dg/cm³
- Emol
11.A solution with a higher concentration in mol/dm³ always contains more moles of solute than a solution with a lower concentration.
Medium
True or false?
12.Match each term with its correct definition.
Medium
- Concentration
- Titration
- Concordant results
- Standard solution
- A solution of accurately known concentration
- The amount of solute dissolved in a given volume of solution
- Titres that agree closely with each other
- A technique used to find the concentration of a solution
13.Place the steps for calculating the concentration of an acid from a titration in the correct order.
Medium
- Calculate the moles of the known solution using moles = concentration × volume
- Use the balanced equation to find the moles of the unknown solution
- Convert the volume of the unknown solution from cm³ to dm³
- Calculate the concentration of the unknown solution using concentration = moles ÷ volume
14.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide was neutralised by 23.5 cm³ of hydrochloric acid. Which of the following statements are correct? (select all that apply)
Hard
- AThe number of moles of NaOH used is 0.00250 mol.
- BThe number of moles of HCl used is 0.00250 mol.
- CThe concentration of the acid is 0.106 mol/dm³.
- DThe concentration of the acid is 0.094 mol/dm³.
- EThe volume of acid must be converted to dm³ before calculating concentration.
15.What is the concentration in mol/dm³ of a solution containing 4.0 g of sodium hydroxide (Mr = 40) in 250 cm³ of solution?
Medium
- A0.10 mol/dm³
- B0.40 mol/dm³
- C0.16 mol/dm³
- D1.60 mol/dm³
16.A student reads a burette from the top of the scale instead of the bottom. What effect will this have on the recorded titre volume?
Medium
- AThe titre will be recorded as too high.
- BThe titre will be recorded as too low.
- CThe titre will be recorded correctly.
- DThe titre will be recorded as zero.
17.What is the concentration in mol/dm³ of a solution containing 0.5 mol of solute in 2 dm³ of solution?
Easy
- A0.25 mol/dm³
- B0.5 mol/dm³
- C1.0 mol/dm³
- D4.0 mol/dm³
18.A solution of sodium chloride has a concentration of 0.50 mol/dm³. What is its concentration in g/dm³? (Mr of NaCl = 58.5)
Medium
- A0.0085 g/dm³
- B29.25 g/dm³
- C58.5 g/dm³
- D117 g/dm³
19.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide was neutralised by 20.0 cm³ of hydrochloric acid. What is the concentration of the hydrochloric acid? (HCl + NaOH → NaCl + H₂O)
Medium
- A0.080 mol/dm³
- B0.125 mol/dm³
- C0.200 mol/dm³
- D0.500 mol/dm³
20.Which of the following statements about titration results are correct? (select all that apply)
Medium
- AConcordant titres are within 0.10 cm³ of each other.
- BAll titre values should be averaged, including any rough trial.
- CA rough titration is used to find the approximate end-point.
- DThe burette should be read from the top of the scale.
- EThe bottom of the meniscus should be read at eye level.
21.To convert a volume from cm³ to dm³, you divide by 1000.
Easy
True or false?
22.Match each term with its correct description.
Medium
- Concentration in mol/dm³
- Concentration in g/dm³
- Titration
- Concordant results
- The number of moles of solute per cubic decimetre of solution
- The mass in grams of solute per cubic decimetre of solution
- A method to find the concentration of a solution using a burette and pipette
- Titre values that are within 0.10 cm³ of each other
23.Place the steps for carrying out a titration in the correct order.
Medium
- Rinse the burette with the solution it will contain.
- Fill the burette with the known solution and record the initial reading.
- Pipette a known volume of the unknown solution into a conical flask.
- Add a few drops of indicator to the conical flask.
- Add the solution from the burette until the indicator changes colour.
- Record the final burette reading and calculate the titre.
24.A student wants to prepare 250 cm³ of a 0.100 mol/dm³ solution of sodium hydroxide. What mass of sodium hydroxide is needed? (Mr of NaOH = 40)
Medium
- A1.00 g
- B0.40 g
- C4.00 g
- D10.0 g
25.In a titration, 25.0 cm³ of 0.200 mol/dm³ sodium hydroxide was neutralised by 20.0 cm³ of sulfuric acid. The equation is H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. What is the concentration of the sulfuric acid?
Medium
- A0.125 mol/dm³
- B0.250 mol/dm³
- C0.100 mol/dm³
- D0.200 mol/dm³
26.Which of the following statements about titration results and calculations are correct? (select all that apply)
Hard
- AConcordant titres are within 0.10 cm³ of each other.
- BThe burette should be read from the top of the scale.
- CThe pipette is used to measure the volume of the solution in the conical flask.
- DThe average titre should include all readings, even non-concordant ones.
- EThe balanced equation is needed to find the mole ratio between the two reactants.
27.A more concentrated solution is always a stronger acid.
Easy
True or false?
28.A student titrated 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide with hydrochloric acid. The equation is HCl + NaOH → NaCl + H₂O. The burette readings were: initial 0.00 cm³, final 23.50 cm³. What is the concentration of the hydrochloric acid?
Hard
- A0.106 mol/dm³
- B0.100 mol/dm³
- C0.0940 mol/dm³
- D0.235 mol/dm³
29.A student carries out a titration and obtains the following titres: 24.60, 23.05, 23.15, 23.30, 23.10 cm³. Concordant results are within 0.10 cm³. Which of the following statements are correct? (select all that apply)
Hard
- AThe concordant titres are 23.05, 23.15, 23.30 and 23.10 cm³.
- BThe mean titre should be calculated using all five results.
- CThe mean titre is 23.15 cm³.
- DThe first titre (24.60 cm³) should be excluded as it is not concordant.
- EThe mean titre is 23.44 cm³.
30.Which of the following is the correct unit for concentration when expressed in moles per unit volume?
Easy
- Amol/dm³
- Bg/dm³
- Cmol
- Ddm³
31.Which of the following is the correct equation for concentration in mol/dm³?
Easy
- Aconcentration = moles of solute / volume of solution in dm³
- Bconcentration = volume of solution in dm³ / moles of solute
- Cconcentration = moles of solute × volume of solution in dm³
- Dconcentration = mass of solute / volume of solution in dm³
32.Which of the following statements about concentration are correct? (select all that apply)
Medium
- AConcentration can be expressed in mol/dm³ or g/dm³.
- BTo convert from cm³ to dm³, you divide by 1000.
- CA more concentrated solution is always a stronger acid.
- DThe concentration of a solution is the amount of solute dissolved in a given volume of solution.
- ETo convert from dm³ to cm³, you divide by 1000.
33.Concentration in mol/dm³ is the number of moles of solute dissolved in 1 dm³ of solution.
Easy
True or false?
34.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide was neutralised by 20.0 cm³ of hydrochloric acid. What is the concentration of the hydrochloric acid?
Medium
- A0.125 mol/dm³
- B0.080 mol/dm³
- C0.200 mol/dm³
- D0.050 mol/dm³
35.Which of the following statements about titration calculations are correct? (select all that apply)
Medium
- AThe balanced equation is needed to find the mole ratio of acid to alkali.
- BThe volume in cm³ must be converted to dm³ before calculating moles.
- CThe concentration of the acid can be calculated without knowing the volume of acid used.
- DConcordant titres should be averaged to improve accuracy.
- EThe burette should be read from the top of the scale for accuracy.
36.Which of the following solutions contains the greatest number of moles of solute?
Medium
- A1 dm³ of 0.5 mol/dm³ solution
- B2 dm³ of 0.3 mol/dm³ solution
- C0.5 dm³ of 1.0 mol/dm³ solution
- D3 dm³ of 0.2 mol/dm³ solution
37.A student measures out a solution using a burette. Which of the following statements about reading a burette are correct? (select all that apply)
Medium
- AThe burette scale should be read at the bottom of the meniscus.
- BThe burette should be read from the top of the scale to get the volume delivered.
- CThe initial and final readings should both be taken to calculate the titre.
- DThe burette should be rinsed with the solution it will contain before use.
- EThe burette reading is always taken from the top of the scale.
38.A student titrates 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide with hydrochloric acid. The equation is HCl + NaOH → NaCl + H₂O. 20.0 cm³ of acid is needed. Which of the following statements are correct? (select all that apply)
Hard
- AThe number of moles of NaOH is 0.00250 mol.
- BThe number of moles of HCl is 0.00200 mol.
- CThe concentration of the acid is 0.125 mol/dm³.
- DThe concentration of the acid is 0.0800 mol/dm³.
- EThe volume of acid in dm³ is 0.0200 dm³.
39.To convert a volume from dm³ to cm³, you multiply by 1000.
Easy
True or false?
40.A solution of potassium hydroxide is made by dissolving 5.6 g of KOH in 500 cm³ of solution. What is the concentration in mol/dm³? (Mr of KOH = 56)
Medium
- A0.10 mol/dm³
- B0.20 mol/dm³
- C0.40 mol/dm³
- D0.80 mol/dm³
41.Convert 0.75 dm³ into cm³.
Easy
42.Complete the sentence about concentration units.
Easy
Concentration can be measured in mol/dm³ or in ____.
43.Name the piece of apparatus used to deliver a variable volume of solution during a titration.
Medium
44.How many moles of solute are present in 250 cm³ of a 0.200 mol/dm³ solution?
Medium
45.Complete the sentence about converting units.
Easy
To convert from cm³ to dm³, you ____ by 1000.
46.Calculate the number of moles of KOH in the solution.
Medium
47.Calculate the concentration of the KOH solution in mol/dm³.
Medium
48.Calculate the concentration of the KOH solution in g/dm³.
Medium
49.How many moles of solute are present in 500 cm³ of a 0.200 mol/dm³ solution?
Medium
50.Convert 2500 cm³ into dm³.
Easy
51.Convert 3.2 dm³ into cm³.
Easy
52.How many moles of sodium hydroxide are present in 1.5 dm³ of a 0.25 mol/dm³ sodium hydroxide solution?
Medium
53.Explain why only concordant titres are averaged when calculating the concentration from a titration.
Hard
54.Explain why it is important to use concordant titres when calculating concentration from a titration.
Hard
55.A student neutralised dilute sulfuric acid with potassium hydroxide solution. The equation is 2KOH + H₂SO₄ → K₂SO₄ + 2H₂O. The student found that 31.0 cm³ of 0.250 mol/dm³ sulfuric acid completely reacted with 25.0 cm³ of potassium hydroxide solution. Calculate the concentration of the potassium hydroxide solution in mol/dm³. You must show your working.
Hard
56.Explain why the student should use a burette rather than a measuring cylinder to measure the volume of acid added during a titration.
Hard
57.Explain why increasing the concentration of hydrochloric acid increases the rate of reaction with magnesium ribbon.
Hard
58.Convert 0.75 dm³ into cm³.
Easy
- A750 cm³
- B675 cm³
- C900 cm³
- D825 cm³
59.How many moles of solute are present in 250 cm³ of a 0.200 mol/dm³ solution?
Medium
- A-0.95 mol
- B1.05 mol
- C0.05 mol
- D2.05 mol
60.A solution of potassium hydroxide is made by dissolving 5.6 g of KOH in 500 cm³ of solution. (Mr of KOH = 56) Calculate the number of moles of KOH in the solution.
Medium
- A0.1 mol
- B-0.9 mol
- C1.1 mol
- D2.1 mol
61.A solution of potassium hydroxide is made by dissolving 5.6 g of KOH in 500 cm³ of solution. (Mr of KOH = 56) Calculate the concentration of the KOH solution in mol/dm³.
Medium
- A1.2 mol/dm³
- B-0.8 mol/dm³
- C0.2 mol/dm³
- D2.2 mol/dm³
62.A solution of potassium hydroxide is made by dissolving 5.6 g of KOH in 500 cm³ of solution, giving a concentration of 0.20 mol/dm³. (Mr of KOH = 56) Calculate the concentration of the KOH solution in g/dm³.
Medium
- A13.2 g/dm³
- B11.2 g/dm³
- C10.2 g/dm³
- D12.2 g/dm³
63.How many moles of solute are present in 500 cm³ of a 0.200 mol/dm³ solution?
Medium
- A0.1 mol
- B2.1 mol
- C1.1 mol
- D-0.9 mol
64.Convert 2500 cm³ into dm³.
Easy
- A2.5 dm³
- B4.5 dm³
- C3.5 dm³
- D1.5 dm³
65.Convert 3.2 dm³ into cm³.
Easy
- A2880 cm³
- B3520 cm³
- C3840 cm³
- D3200 cm³
66.How many moles of sodium hydroxide are present in 1.5 dm³ of a 0.25 mol/dm³ sodium hydroxide solution?
Medium
- A-0.625 mol
- B2.375 mol
- C0.375 mol
- D1.375 mol

Thẻ ghi nhớ

What is the equation linking concentration (in mol/dm³), moles of solute and volume of solution?

concentration (mol/dm³) = moles of solute (mol) ÷ volume of solution (dm³)

How do you convert a volume from cm³ to dm³?

Divide the volume in cm³ by 1000. For example, 500 cm³ = 0.5 dm³.

How do you convert a volume from dm³ to cm³?

Multiply the volume in dm³ by 1000. For example, 2.5 dm³ = 2500 cm³.

What is the mass of 1 mole of sodium hydroxide, NaOH? (Ar: Na=23, O=16, H=1)

40 g. Mr = 23 + 16 + 1 = 40, so 1 mol NaOH has a mass of 40 g.

Calculate the number of moles in 2.5 dm³ of a solution with concentration 0.2 mol/dm³.

Moles = concentration × volume = 0.2 × 2.5 = 0.5 mol.

Calculate the concentration of a solution when 80 g of NaOH is dissolved in 500 cm³ of water. (Mr NaOH = 40)

80 g NaOH = 2 mol; 500 cm³ = 0.5 dm³; concentration = 2 ÷ 0.5 = 4 mol/dm³.

In a titration, 25.0 cm³ of hydrochloric acid is neutralised by 12.1 cm³ of 0.100 mol/dm³ NaOH. What is the concentration of the acid?

Moles NaOH = 0.0121 dm³ × 0.100 = 1.21 × 10⁻³ mol. The 1:1 equation means moles HCl = 1.21 × 10⁻³ mol. Concentration HCl = 1.21 × 10⁻³ ÷ 0.0250 = 0.0484 mol/dm³.

What is a standard solution?

A solution of accurately known concentration, prepared by dissolving an exact mass of solute in a known volume of solution.

Why is a burette used to measure the volume of solution added in a titration?

A burette allows the volume added to be measured accurately and can be added drop by drop, so the end-point can be reached precisely.

What are concordant results in a titration?

Titres that are within 0.10 cm³ of each other. Only concordant results should be averaged to improve accuracy.

Why should you not average non-concordant titres?

Non-concordant titres are not reliable and averaging them would give an inaccurate mean, leading to an incorrect calculated concentration.

What is the relationship between concentration in mol/dm³ and concentration in g/dm³?

concentration (g/dm³) = concentration (mol/dm³) × molar mass (g/mol).

What is the concentration in g/dm³ of a 0.25 mol/dm³ solution of sodium hydroxide? (Mr NaOH = 40)

0.25 × 40 = 10 g/dm³.

How many moles of sodium hydroxide are present in 1.5 dm³ of a 0.25 mol/dm³ solution?

Moles = concentration × volume = 0.25 × 1.5 = 0.375 mol.

In a titration, why is a pipette used to measure the volume of the solution in the conical flask?

A pipette measures a fixed, accurate volume (e.g. 25.0 cm³) so the amount of substance in the flask is known precisely.

What is the balanced symbol equation, including state symbols, for the reaction between hydrochloric acid and sodium hydroxide?

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

In a titration, 25.0 cm³ of dilute hydrochloric acid is neutralised by 23.5 cm³ of 0.100 mol/dm³ sodium hydroxide. Calculate the concentration of the acid.

Moles NaOH = 0.0235 dm³ × 0.100 = 0.00235 mol. The 1:1 equation means moles HCl = 0.00235 mol. Concentration HCl = 0.00235 ÷ 0.0250 = 0.094 mol/dm³.

Balance the equation: ___ KOH + ___ H₂SO₄ → ___ K₂SO₄ + ___ H₂O

2 KOH + H₂SO₄ → K₂SO₄ + 2 H₂O

31.0 cm³ of 0.250 mol/dm³ sulfuric acid completely reacts with 25.0 cm³ of potassium hydroxide solution. Calculate the concentration of the KOH solution in mol/dm³.

Moles H₂SO₄ = 0.0310 × 0.250 = 0.00775 mol. From 2KOH + H₂SO₄, moles KOH = 2 × 0.00775 = 0.0155 mol. Concentration KOH = 0.0155 ÷ 0.0250 = 0.62 mol/dm³.

What mass of barium chloride is needed to make 250 cm³ of a 0.150 mol/dm³ solution? (Mr BaCl₂ = 208)

Moles = 0.250 dm³ × 0.150 = 0.0375 mol. Mass = 0.0375 × 208 = 7.8 g.

A solution of sulfuric acid contains 9.8 g of H₂SO₄ in 250 cm³. What is its concentration in mol/dm³? (Mr H₂SO₄ = 98)

Moles = 9.8 ÷ 98 = 0.10 mol. Volume = 0.250 dm³. Concentration = 0.10 ÷ 0.250 = 0.40 mol/dm³.

How much solute is present in 2 dm³ of a 0.5 mol/dm³ solution of potassium iodide?

Moles = concentration × volume = 0.5 × 2 = 1.0 mol.

25.00 cm³ of 0.20 mol/dm³ sodium hydroxide reacts with 26.50 cm³ of hydrochloric acid. What is the concentration of the acid?

Moles NaOH = 0.02500 × 0.20 = 0.00500 mol. The 1:1 equation means moles HCl = 0.00500 mol. Concentration HCl = 0.00500 ÷ 0.02650 = 0.19 mol/dm³.

What mass of sodium hydroxide is required to make 250 cm³ of a 0.150 mol/dm³ solution? (Mr NaOH = 40)

Moles = 0.250 dm³ × 0.150 = 0.0375 mol. Mass = 0.0375 × 40 = 1.5 g.

Why is it important to convert cm³ to dm³ before using the concentration formula?

The concentration formula uses volume in dm³. If cm³ is used without converting, the answer will be 1000 times too large.

In a titration, what is the end-point?

The point at which the indicator changes colour, showing that the reaction is just complete.

Explain why increasing the concentration of a reactant increases the rate of reaction.

A higher concentration means more particles in the same volume, so collisions are more frequent, increasing the rate.

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