How Much? The Amount Of Chemical Change

விளையாடிக் கற்றுக்கொள்ளுங்கள்

ஆற்றல் சம்பாதிக்க இந்த கேள்விகளுக்குப் பதிலளியுங்கள், பின்னர் மீன் பிடித்து ஆராயுங்கள். கணக்கு தேவையில்லை.

கல்வியாளர்களுக்கு: How Much? The Amount Of Chemical Change (Chemistry, SL)-க்கான தயாரான பாட ஸ்லைடுகள், திருப்புதல் குறிப்புகள் — உங்கள் பாடத்தில் அவற்றைப் பயன்படுத்தவும், அல்லது கற்பவர்கள் நேரலை விளையாட்டாக விளையாடும் ஊடாடும் வகுப்பு செயல்பாடாக தலைப்பை இயக்கவும்.

பாட குறிப்புகள்

Balancing Equations

A symbol equation uses chemical symbols to show the number and type of atoms in reactants and products; a word equation uses only words.
Atoms cannot be created or destroyed in a chemical reaction, so the number of each atom must be the same on both sides — the equation must be balanced.
When balancing: never change any chemical formulae; put numbers in front of formulae; do not split polyatomic ions (like SO₄²⁻ or NO₃⁻) if they appear unchanged on both sides.
For combustion of organic compounds, balance carbon first, then hydrogen, then oxygen.
Use state symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous.
Some elements are diatomic in their natural state and must be written with a subscript 2: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂.

A balanced chemical equation

Reacting Mass Calculations

The number of moles is calculated using: number of moles = mass of substance (g) / molar mass (g mol⁻¹).
Be clear about the particle: 1 mole of CaF₂ contains 1 mole of CaF₂ formula units, but 1 mole of Ca²⁺ ions and 2 moles of F⁻ ions.
The stoichiometry (mole ratio) from the balanced equation links the amounts of reactants and products.
To find the mass of product: calculate moles of reactant, use the mole ratio, then convert moles to mass using mass = moles × molar mass.
You can work in any mass unit (grams, tonnes, etc.) as long as you are consistent, because reacting masses are in proportion to the balanced equation.

Avogadro's Law & Molar Volume of Gas

Avogadro's Law states that equal volumes of gases contain the same number of molecules, so gas volume ratios equal mole ratios.
At STP (0 °C and 100 kPa), one mole of any gas occupies 22.7 dm³ mol⁻¹.
Volume of gas = amount of gas (mol) × 22.7 dm³ mol⁻¹; amount of gas (mol) = volume of gas (dm³) / 22.7 dm³ mol⁻¹.
To convert cm³ to dm³, divide by 1000.
In gas reactions, identify the limiting reactant first if volumes are not in the same ratio as the coefficients.
Quick method to find limiting reactant: divide the moles (or volumes) of each reactant by its coefficient; the smallest result is the limiting reactant.

Concentration Calculations

Volumetric analysis uses a standard solution of known concentration to find the concentration of an unknown solution, usually by titration.
In a titration, a known volume (e.g. 20 or 25 cm³) is measured with a pipette into a conical flask; the other solution is added from a burette until the indicator changes colour.
Multiple trials are carried out until concordant results are obtained (within a small range).
The four steps: write the balanced equation; calculate moles of the known substance; use the mole ratio; calculate the unknown amount/concentration/volume.
Concentration (mol dm⁻³) = moles / volume (dm³); moles = concentration × volume (dm³).
For monoprotic acid–base reactions, the shortcut C₁V₁ = C₂V₂ can be used (volumes in cm³ are fine as units cancel).
Back titration: react the unknown with an excess of a reagent, then titrate the excess to find the amount of the original substance.

Concentration, moles and volume

Limiting & Excess Reactants

The limiting reactant is the reactant that is completely used up and determines the amount of product formed.
The excess reactant is the reactant that is not completely used up and is left over at the end.
To find the limiting reactant: calculate moles of each reactant, then divide each by its coefficient from the balanced equation; the smallest result is limiting.
Alternatively, compare the required mole ratio: calculate how much of one reactant is needed to fully react with the other and see which runs out first.

Percentage Yield Calculations

The theoretical yield is the maximum amount of product possible from the limiting reactant, assuming perfect conversion.
The experimental (actual) yield is the amount of product actually collected in the lab.
Percentage yield = (actual yield / theoretical yield) × 100.
The limiting reactant must be identified first to calculate the correct theoretical yield.
Differences between theoretical and actual yield arise from side reactions, loss during transfer or purification, and incomplete reaction.
Ensure actual and theoretical yields are in the same units before calculating percentage yield.

Atom Economy

Atom economy measures how efficiently reactants are converted into the desired product.
Atom economy = (molecular mass of desired product / sum of molecular masses of all reactants) × 100.
Alternatively, atom economy = (mass of desired product / total mass of all products) × 100.
Addition reactions always have 100% atom economy because all reactant atoms end up in the single product (e.g. CH₂=CH₂ + Br₂ → CH₂BrCH₂Br).
A low atom economy means more waste and by-products, leading to higher environmental and economic costs.
Atom economy is calculated from the balanced equation, not from experimental data.
Other factors for process efficiency include rate, quantities of catalysts and solvents, energy use, and economic efficiency.

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1.Which of the following is the correct definition of the term 'limiting reactant'?
Easy
- AThe reactant that is completely used up in a reaction and determines the amount of product formed
- BThe reactant that is left over at the end of a reaction
- CThe reactant that is present in the largest amount by mass
- DThe reactant that is present in the largest amount by moles
2.In a chemical reaction, atoms are created or destroyed.
Easy
True or false?
3.Which of the following statements about atom economy are correct? (select all that apply)
Easy
- AIt is a measure of how efficiently a reaction converts reactants into the desired product.
- BIt is calculated using experimental data.
- CAddition reactions typically have an atom economy of 100%.
- DA low atom economy means less waste is produced.
- EIt can be calculated using the formula: (molecular mass of desired product / sum of molecular masses of all reactants) × 100.
4.A student calculates the percentage yield of a reaction. The theoretical yield is 6.5 g and the actual yield is 5.8 g. What is the percentage yield?
Medium
- A89.2%
- B112%
- C10.8%
- D89.2 g
5.A sample of marble contains calcium carbonate. 27.20 cm³ of 0.200 mol dm⁻³ HCl was added to 0.188 g of marble. The excess acid required 23.80 cm³ of 0.100 mol dm⁻³ NaOH for neutralisation. What is the percentage by mass of calcium carbonate in the marble?
Medium
- A81.5%
- B18.5%
- C40.8%
- D95.0%
6.In a titration, concordant results are those that are within a small range of each other, typically within 0.10 cm³.
Easy
True or false?
7.Match each term with its correct definition.
Easy
- Limiting reactant
- Theoretical yield
- Atom economy
- The maximum amount of product that can be formed from a given amount of reactants, assuming perfect conversion.
- A measure of how efficiently a reaction converts reactants into the desired product.
- The reactant that is completely used up in a reaction and determines the amount of product formed.
8.Place the following steps in the correct order for carrying out a titration.
Easy
- Rinse the burette with the solution it will contain and fill it.
- Measure a known volume of the solution into a conical flask using a pipette.
- Add a few drops of indicator to the conical flask.
- Slowly add the solution from the burette until the indicator changes colour.
- Repeat the titration until concordant results are obtained.

மேலும் கேள்விகள்

9.Which of the following statements about Avogadro's Law and molar gas volume are correct? (select all that apply)
Medium
- AAt STP, one mole of any gas occupies 22.7 dm³.
- BEqual volumes of gases at the same temperature and pressure contain the same number of molecules.
- CThe molar gas volume is directly proportional to the molar mass of the gas.
- DAt STP, the conditions are 0 °C and 100 kPa.
- EThe molar gas volume at STP is 24.0 dm³ mol⁻¹.
10.Place the following steps in the correct order for calculating reacting masses.
Medium
- Write the balanced chemical equation.
- Calculate the number of moles of the known substance.
- Use the mole ratio from the equation to find moles of the unknown substance.
- Convert moles of the unknown substance to mass using its molar mass.
11.Which of the following are correct steps when balancing a chemical equation? (select all that apply)
Medium
- AChange the subscripts in a formula to balance atoms.
- BPlace coefficients in front of the chemical formulae.
- CBalance carbon, then hydrogen, then oxygen in combustion reactions.
- DSplit polyatomic ions into individual atoms whenever they appear.
- EInclude state symbols after balancing.
12.The limiting reactant is the reactant that is completely used up in a chemical reaction.
Easy
True or false?
13.What is the volume occupied by 2.0 moles of nitrogen gas at STP?
Easy
- A22.7 dm³
- B45.4 dm³
- C11.35 dm³
- D2.0 dm³
14.In a titration, 25.0 cm³ of 0.100 mol dm⁻³ sodium hydroxide is neutralised by 20.0 cm³ of hydrochloric acid. What is the concentration of the hydrochloric acid?
Medium
- A0.080 mol dm⁻³
- B0.125 mol dm⁻³
- C0.100 mol dm⁻³
- D0.200 mol dm⁻³
15.A reaction has a theoretical yield of 10.0 g and an actual yield of 7.5 g. What is the percentage yield?
Medium
- A75%
- B133%
- C7.5%
- D25%
16.In the reaction 2Mg (s) + O₂ (g) → 2MgO (s), what is the mole ratio of magnesium to oxygen?
Medium
- A1:2
- B2:1
- C1:1
- D2:3
17.Calculate the mass of magnesium oxide produced when 6.0 g of magnesium is completely burned in oxygen. (Ar: Mg = 24.31, O = 16.00)
Medium
- A8.0 g
- B10.0 g
- C12.0 g
- D16.0 g
18.What volume of 1.50 mol dm⁻³ hydrochloric acid is required to react completely with 2.00 g of calcium carbonate? CaCO₃ (s) + 2HCl (aq) → CaCl₂ (aq) + CO₂ (g) + H₂O (l). (Mr: CaCO₃ = 100.09)
Medium
- A13.3 cm³
- B26.6 cm³
- C53.2 cm³
- D0.0266 cm³
19.What is the volume occupied by 3.0 moles of hydrogen gas at STP? (Molar gas volume at STP = 22.7 dm³ mol⁻¹)
Medium
- A22.7 dm³
- B45.4 dm³
- C68.1 dm³
- D7.57 dm³
20.How many moles are in 960 cm³ of sulfur dioxide gas at STP? (Molar gas volume at STP = 22.7 dm³ mol⁻¹)
Medium
- A4.22 × 10⁻² mol
- B0.422 mol
- C2.37 × 10⁻² mol
- D4.22 × 10⁻⁵ mol
21.25.0 cm³ of 0.050 mol dm⁻³ sodium carbonate was completely neutralised by 20.0 cm³ of dilute hydrochloric acid. Calculate the concentration of the hydrochloric acid. Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
Medium
- A0.050 mol dm⁻³
- B0.125 mol dm⁻³
- C0.250 mol dm⁻³
- D0.0625 mol dm⁻³
22.A student added 27.20 cm³ of 0.200 mol dm⁻³ HCl to 0.188 g of marble. The excess acid required 23.80 cm³ of 0.100 mol dm⁻³ NaOH for neutralisation. Calculate the percentage of calcium carbonate in the marble. (Mr: CaCO₃ = 100.09)
Hard
- A81.5%
- B75.0%
- C90.0%
- D18.5%
23.What is the limiting reactant when 10 mol of carbon reacts with 3 mol of hydrogen? C + 2H₂ → CH₄
Medium
- ACarbon
- BHydrogen
- CBoth are limiting
- DNeither is limiting
24.In a back titration, the percentage by mass of calcium carbonate in a marble sample is determined by adding a measured excess of hydrochloric acid, then titrating the acid that remains with sodium hydroxide. Why is an excess of acid used?
Medium
- ATo ensure that all of the calcium carbonate in the marble reacts
- BTo make the sodium hydroxide react faster in the titration
- CTo neutralise the sodium hydroxide before the titration begins
- DTo prevent carbon dioxide from escaping from the flask
25.A student records the following burette readings for a titration: final reading 25.45 cm³, initial reading 0.05 cm³. What is the titre?
Medium
- A25.40 cm³
- B25.50 cm³
- C25.45 cm³
- D25.00 cm³
26.Which of the following statements about back titrations are correct? (select all that apply)
Medium
- AAn excess of one reactant is added to the unknown substance
- BThe excess reactant remaining is determined by titration
- CThe unknown substance is always the limiting reactant in the first reaction
- DBack titrations can be used when the direct reaction is too slow to titrate directly
- EThe mole ratio from the balanced equation is not needed in a back titration
27.When calculating an average titre from burette readings, the final answer should be rounded to two decimal places because the readings are recorded to two decimal places.
Easy
True or false?
28.Match each titration term with its correct description.
Medium
- Concordant results
- Titre
- Back titration
- Standard solution
- Titres within a small range of each other, typically within 0.10 cm³
- The volume of solution delivered from the burette
- A method where excess reactant is added and the remaining excess is titrated
- A solution of accurately known concentration
29.Using the mole ratio from the equation, which reactant is the limiting reagent and why?
Medium
- ACopper(II) sulfate, because 0.00801 mol requires 0.00534 mol of Al and more Al is available
- BAluminium, because 0.00927 mol requires 0.00618 mol of CuSO₄·5H₂O and less is available
- CCopper(II) sulfate, because it has the larger molar mass
- DAluminium, because it is the metal
30.A student uses the back titration method to find the percentage of calcium carbonate in marble. Which of the following errors would cause the calculated percentage of calcium carbonate to be too high? (select all that apply)
Hard
- AThe burette is rinsed with water and not with sodium hydroxide solution
- BThe conical flask is rinsed with water before adding the acid and marble
- CSome of the calcium carbonate sample is lost during transfer to the flask
- DThe burette reading is taken from the top of the meniscus instead of the bottom
- EThe sodium hydroxide solution is more concentrated than stated on the label
31.Place the steps of a back titration to find the percentage of calcium carbonate in marble in the correct order.
Medium
- Weigh a sample of marble and place it in a conical flask
- Add a measured excess of hydrochloric acid and allow the reaction to finish
- Titrate the remaining acid with standard sodium hydroxide solution
- Calculate the amount of acid that reacted with the marble by subtracting the excess from the total added
- Calculate the moles and mass of calcium carbonate and hence the percentage in the marble
32.In a titration, the burette should be rinsed with the solution it will contain before use.
Easy
True or false?
33.A student calculates the percentage yield of a reaction as 84.5%. The theoretical yield is 0.509 g. What mass of product was actually collected?
Medium
- A0.430 g
- B0.601 g
- C0.509 g
- D0.845 g
34.Which of the following is a shorthand way of describing a chemical reaction using chemical symbols to show the number and type of each atom in the reactants and products?
Easy
- AA symbol equation
- BA word equation
- CA state symbol
- DA molar ratio
35.During chemical reactions, atoms cannot be created or destroyed.
Easy
True or false?
36.Which of the following is the correct state symbol for a substance dissolved in water?
Easy
- A(s)
- B(l)
- C(g)
- D(aq)
37.Which of the following elements are diatomic in their natural state and must be written with a subscript 2 in equations? (select all that apply)
Medium
- AHydrogen
- BNitrogen
- COxygen
- DFluorine
- ESodium
38.Which of the following is the correct definition of the term 'theoretical yield'?
Medium
- AThe amount of product actually collected in the laboratory
- BThe maximum amount of product that can be formed from a given amount of reactants, assuming perfect conversion with no losses
- CThe amount of limiting reactant used up in a reaction
- DThe mass of all reactants used in a reaction
39.Which of the following is the correct definition of 'atom economy'?
Medium
- AThe proportion of the total mass of reactants that ends up in the useful product
- BThe amount of product actually collected in the laboratory
- CThe maximum amount of product that can be formed from a given amount of reactants
- DThe reactant that is completely used up in a reaction
40.In addition reactions, the atom economy is always 100%.
Easy
True or false?
41.Complete the following sentence about Avogadro's Law.
Easy
At standard temperature and pressure (STP), one mole of any gas occupies a volume of ____ dm³.
42.What is the term for the maximum amount of product that can be formed from a given amount of reactants, assuming perfect conversion with no losses?
Easy
43.Calculate the volume, in dm³, occupied by 3.0 moles of hydrogen gas at STP.
Medium
44.Calculate the number of moles in 7.2 dm³ of carbon monoxide at STP.
Medium
45.Complete the statement about atom economy.
Easy
Atom economy = (molecular mass of ____ / sum of molecular masses of all ____) × 100
46.What is the term for the reactant that limits the amount of product formed in a chemical reaction?
Medium
47.Calculate the mass, in grams, of potassium nitrate required to produce 1.5 g of oxygen. 2KNO₃ → 2KNO₂ + O₂. (Mr: KNO₃ = 101.1, O₂ = 32.0). Give your answer to 2 significant figures.
Medium
48.Using the mean titre of 21.88 cm³ and a hydrochloric acid concentration of 0.10 mol dm⁻³, calculate the amount, in moles, of hydrochloric acid used. Give your answer to 2 decimal places.
Medium
49.A canister contains 5.00 g of potassium superoxide, KO₂. Calculate the amount, in moles, of KO₂ in the canister. Give your answer to 3 significant figures. (Ar: K = 39.10, O = 16.00)
Medium
50.Using your answer of 0.0703 mol of KO₂ and the equation 4KO₂ (s) + 2CO₂ (g) → 2K₂CO₃ (s) + 3O₂ (g), calculate the volume, in dm³, of carbon dioxide at STP that can be removed from the air. Give your answer to 3 significant figures. (Molar gas volume at STP = 22.7 dm³ mol⁻¹)
Medium
51.During a test of the superoxide canister, 2.61 g of potassium carbonate was produced. The maximum theoretical yield was calculated to be 4.86 g. Calculate the percentage yield of potassium carbonate. Give your answer to 3 significant figures.
Medium
52.The concentration of sodium thiosulfate solution was 0.120 mol dm⁻³ and the mean titre was 21.90 cm³. Calculate the amount, in moles, of sodium thiosulfate used in the titration. Give your answer to 3 significant figures.
Medium
53.Explain the meaning of 'ppm' in the context of an aqueous solution.
Hard
54.Explain why the percentage yield of a reaction is often less than 100%.
Hard
55.Explain why the hydration of ethene has a higher atom economy than the substitution of bromoethane to produce ethanol.
Hard
56.Explain why a back titration is used to determine the percentage of calcium carbonate in a sample of marble, rather than titrating the marble directly with hydrochloric acid.
Medium
57.A student determines the percentage yield of copper in a displacement reaction. State and explain two practical errors that would cause the percentage yield to be lower than the true value.
Hard
58.Calculate the volume, in dm³, occupied by 3.0 moles of hydrogen gas at STP.
Medium
- A81.7 dm³
- B74.9 dm³
- C61.3 dm³
- D68.1 dm³
59.Calculate the number of moles in 7.2 dm³ of carbon monoxide at STP.
Medium
- A2.32 mol
- B-0.68 mol
- C0.32 mol
- D1.32 mol
60.Calculate the mass, in grams, of potassium nitrate required to produce 1.5 g of oxygen. 2KNO₃ → 2KNO₂ + O₂. (Mr: KNO₃ = 101.1, O₂ = 32.0). Give your answer to 2 significant figures.
Medium
- A10.5 g
- B11.5 g
- C8.5 g
- D9.5 g
61.Using the mean titre of 21.88 cm³ and a hydrochloric acid concentration of 0.10 mol dm⁻³, calculate the amount, in moles, of hydrochloric acid used. Give your answer to 2 decimal places.
Medium
- A2.0022 mol
- B1.0022 mol
- C-0.9978 mol
- D0.0022 mol
62.A canister contains 5.00 g of potassium superoxide, KO₂. Calculate the amount, in moles, of KO₂ in the canister. Give your answer to 3 significant figures. (Ar: K = 39.10, O = 16.00)
Medium
- A-0.9297 mol
- B1.0703 mol
- C2.0703 mol
- D0.0703 mol
63.Using your answer of 0.0703 mol of KO₂ and the equation 4KO₂ (s) + 2CO₂ (g) → 2K₂CO₃ (s) + 3O₂ (g), calculate the volume, in dm³, of carbon dioxide at STP that can be removed from the air. Give your answer to 3 significant figures. (Molar gas volume at STP = 22.7 dm³ mol⁻¹)
Medium
- A0.798 dm³
- B1.798 dm³
- C-0.202 dm³
- D2.798 dm³
64.During a test of the superoxide canister, 2.61 g of potassium carbonate was produced. The maximum theoretical yield was calculated to be 4.86 g. Calculate the percentage yield of potassium carbonate. Give your answer to 3 significant figures.
Medium
- A53.7 %
- B64.5 %
- C48.3 %
- D59.1 %
65.The concentration of sodium thiosulfate solution was 0.120 mol dm⁻³ and the mean titre was 21.90 cm³. Calculate the amount, in moles, of sodium thiosulfate used in the titration. Give your answer to 3 significant figures.
Medium
- A1.0026 mol
- B0.00263 mol
- C-0.9974 mol
- D2.0026 mol

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