Experimental Techniques

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Notes de leçon

Apparatus for Measurements

Time is measured with a stopwatch or stopclock, accurate to one or two decimal places; units are seconds or minutes.
Temperature is measured with a thermometer (precision ±0.5 °C) or digital temperature probe (precision ±0.1 °C); units are degrees Celsius (°C).
Mass is measured using a digital balance (usually to two decimal places); balance must be tared before use and allowed to settle.
Volume of liquid is measured with burettes (most accurate for variable volumes, 0–50 cm³), volumetric pipettes (most accurate for fixed volumes, e.g. 10 cm³ or 25 cm³), or measuring cylinders (for approximate volumes).
Volume of gas is measured using a gas syringe (more precise) or by downward displacement of water (not suitable for soluble gases).
When reading a burette, read from the bottom of the meniscus; the scale runs from 0.00 cm³ at the top to 50.00 cm³ at the bottom.

Apparatus for measuring volume

Solutions

Solvent: the liquid in which a solute dissolves (e.g. water in seawater).
Solute: the substance that dissolves in a solvent (e.g. salt in seawater).
Solution: the mixture formed when a solute dissolves in a solvent (e.g. seawater).
Saturated solution: contains the maximum concentration of solute dissolved at a given temperature.
Soluble substances dissolve; insoluble substances do not dissolve.
Filtrate: the liquid that passes through a filter; residue: the solid left behind after filtration or evaporation.

Acid-Base Titrations

Titration determines the concentration of an acid or alkali by neutralisation; can also be used to prepare salts.
Apparatus: 25 cm³ volumetric pipette, pipette filler, 50 cm³ burette, 250 cm³ conical flask, funnel, indicator, clamp stand, white tile.
Method: pipette a fixed volume of alkali into a conical flask, add indicator, then add acid from the burette while swirling until the endpoint (sharp colour change).
Record burette readings to the nearest 0.05 cm³; repeat until two concordant results (within 0.1 cm³) are obtained.
Common indicators: methyl orange (red in acid, yellow in alkali, orange at endpoint) and phenolphthalein (colourless in acid, pink in alkali).
Common errors: not removing the funnel from the burette, not filling the jet space, and reading the burette from the top of the meniscus.

Titration apparatus set-up

Diapos

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1.Which piece of apparatus is most accurate for measuring a variable volume of liquid between 0 and 50 cm³?
Easy
- AMeasuring cylinder
- BBurette
- CVolumetric pipette
- DGas syringe
2.A volumetric pipette is used to measure a fixed volume of liquid accurately.
Easy
True or false?
3.A stopwatch displays 1:30 (minutes:seconds). What is the time in seconds?
Easy
- A99
- B81
- C90
- D108
4.Complete the sentence about titration.
Easy
The endpoint is reached when one drop causes a sharp ____ change.
5.Match each indicator to its colour in acid.
Medium
- Methyl orange
- Phenolphthalein
- Litmus
- Red
- Colourless
- Red
6.Arrange the following steps in a titration in the correct order.
Medium
- Add indicator to conical flask
- Fill burette with acid
- Record initial burette reading
- Perform rough titration
7.Which of the following is the most accurate way to measure a fixed volume of liquid?
Easy
- AMeasuring cylinder
- BBurette
- CVolumetric pipette
- DBeaker
8.What term describes a solution that contains the maximum concentration of solute at a given temperature?
Easy

Plus de questions

9.Complete the sentence about burette reading.
Easy
When reading a burette, the bottom of the ____ is used to determine the volume.
10.Match each piece of apparatus to its most appropriate use for measuring volume.
Medium
- Burette
- Volumetric pipette
- Measuring cylinder
- Measuring a fixed volume accurately
- Measuring variable volumes precisely
- Measuring approximate volumes
11.Arrange the following steps of a titration in the correct order.
Medium
- Add indicator to the conical flask
- Fill the burette with acid and record initial reading
- Use a pipette to transfer alkali to the flask
- Titrate until the indicator changes colour
- Repeat until concordant results are obtained
12.A saturated solution contains the maximum possible concentration of solute at a given temperature.
Easy
True or false?
13.A student reads a burette and records the volume as 23.5 cm³. What is the correct reading to the nearest 0.05 cm³?
Medium
- A23.50 cm³
- B23.55 cm³
- C23.45 cm³
- D23.5 cm³
14.Which of the following are common errors during a titration? (Select all that apply)
Medium
- ANot removing the funnel from the burette
- BFilling the jet space of the burette
- CReading the volume from the top of the meniscus
- DSwirling the flask vigorously
15.Place the following steps for measuring a fixed volume of liquid using a volumetric pipette in the correct order.
Medium
- Attach a pipette filler to the pipette
- Draw liquid above the graduation mark
- Release the filler and let the liquid drain until the bottom of the meniscus touches the mark
- Transfer the liquid to the receiving vessel
16.Which piece of apparatus is most precise for measuring the volume of gas produced in a reaction?
Medium
- AGas syringe
- BMeasuring cylinder
- CDownward displacement of water
- DBurette
17.Which of the following statements about measuring mass are correct? (Select all that apply)
Medium
- AA digital balance should be tared before use.
- BMass is measured in grams or kilograms.
- CThe balance reading should be recorded immediately without waiting.
- DA balance should be allowed to settle before recording the reading.
18.Which of the following are suitable indicators for an acid-base titration? (Select all that apply)
Medium
- AMethyl orange
- BLitmus solution
- CPhenolphthalein
- DThymolphthalein
- ERed litmus paper
19.In a titration, a student forgets to remove the funnel from the top of the burette after filling. How does this affect the titre volume?
Medium
- AThe titre volume will be higher than the true value
- BThe titre volume will be lower than the true value
- CThe titre volume will be unaffected
- DThe indicator will change colour too early
20.A volumetric pipette is the most accurate piece of apparatus for measuring a variable volume of liquid.
Easy
True or false?
21.Which of the following are common errors during a titration that could lead to an inaccurate titre volume? (Select all that apply)
Medium
- ANot removing the funnel from the top of the burette after filling
- BReading the burette from the top of the meniscus
- CUsing a pipette filler to draw up the alkali
- DNot filling the jet space of the burette before starting
- ESwirling the conical flask during the addition of acid
22.A stopwatch is used to measure temperature.
Easy
True or false?
23.Which piece of apparatus is most accurate for measuring a fixed volume of liquid?
Easy
- AMeasuring cylinder
- BBurette
- CVolumetric pipette
- DBeaker
24.A saturated solution contains the maximum concentration of solute at a given temperature.
Easy
True or false?
25.In a titration, which indicator gives a colour change from colourless to pink at the endpoint?
Easy
- AMethyl orange
- BPhenolphthalein
- CLitmus
- DThymolphthalein
26.A student measures the time for a reaction using a stopwatch. The display shows 2:45 (minutes:seconds). What is the time in seconds?
Easy
- A165 seconds
- B145 seconds
- C2.45 seconds
- D245 seconds
27.Which of the following are suitable indicators for a strong acid-strong base titration? (Select all that apply)
Medium
- AMethyl orange
- BPhenolphthalein
- CLitmus
- DThymolphthalein
- EUniversal indicator
28.Match each term to its correct definition.
Easy
- Solute
- Solvent
- Solution
- The liquid in which a solute dissolves
- The substance that dissolves in a liquid
- The mixture formed when a solute dissolves in a solvent
29.A student uses a measuring cylinder to measure 25 cm³ of water, then pours it into a beaker. Which statement about the accuracy of this measurement is correct?
Medium
- AThe measuring cylinder gives a more accurate volume than a volumetric pipette.
- BThe measuring cylinder gives an approximate volume; a volumetric pipette would be more accurate.
- CThe beaker is more accurate than the measuring cylinder.
- DThe volume is exactly 25.00 cm³.
30.Which of the following is the most suitable indicator for a titration between a strong acid and a strong base?
Medium
- ALitmus
- BMethyl orange
- CPhenolphthalein
- DBoth methyl orange and phenolphthalein
31.Which of the following are common errors during a titration that can lead to an inaccurate titre volume? (Select all that apply)
Medium
- ANot removing the funnel from the top of the burette after filling
- BReading the burette from the top of the meniscus
- CRinsing the conical flask with the solution to be titrated
- DUsing a white tile under the conical flask
- EFilling the jet space of the burette before taking the initial reading
32.Arrange the following steps for measuring a fixed volume of liquid using a volumetric pipette in the correct order. (Order from first to last)
Medium
- Attach a pipette filler to the top of the pipette
- Squeeze the pipette filler to expel air
- Draw liquid above the graduation mark
- Allow liquid to drain until the bottom of the meniscus aligns with the mark
- Transfer the liquid to the receiving vessel by releasing the filler
33.A gas syringe is more precise than downward displacement of water for measuring the volume of a gas produced in a reaction.
Easy
True or false?
34.In a titration, 25.0 cm³ of sodium hydroxide solution is neutralised by 22.5 cm³ of hydrochloric acid of concentration 0.100 mol/dm³. Calculate the concentration of the sodium hydroxide solution in mol/dm³.
Hard
35.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide solution neutralises 20.0 cm³ of hydrochloric acid. Calculate the concentration of the hydrochloric acid in mol/dm³.
Medium
36.Complete the sentences about solution terminology.
Easy
The substance that dissolves in a liquid is called the ____. The liquid in which it dissolves is the ____. The mixture formed is a ____.
37.Complete the sentence about indicators.
Easy
Phenolphthalein is colourless in ____ solution and turns ____ in alkaline solution.
38.A burette reading is taken from the top of the meniscus. The bottom of the meniscus is at 23.4 cm³ and the top is at 23.7 cm³. What is the correct reading to the nearest 0.05 cm³?
Medium
39.What is the name of the liquid that passes through a filter paper during filtration?
Easy
40.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide solution is neutralised by 22.5 cm³ of hydrochloric acid. Calculate the concentration of the hydrochloric acid in mol/dm³.
Medium
41.A stopwatch display shows 2:30 (minutes:seconds). What is the time in seconds?
Easy
42.Describe how you would measure the volume of a gas produced in a reaction using a gas syringe.
Easy
43.In a titration, a student forgets to remove the funnel from the top of the burette after filling. Explain how this affects the titre volume.
Medium
44.In a titration, 25.0 cm³ of sodium hydroxide solution is neutralised by 22.5 cm³ of hydrochloric acid of concentration 0.100 mol/dm³. Calculate the concentration of the sodium hydroxide solution in mol/dm³.
Medium
- A0.09 mol/dm³
- B1.09 mol/dm³
- C2.09 mol/dm³
- D-0.91 mol/dm³
45.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide solution neutralises 20.0 cm³ of hydrochloric acid. Calculate the concentration of the hydrochloric acid in mol/dm³.
Medium
- A-0.875 mol/dm³
- B2.125 mol/dm³
- C0.125 mol/dm³
- D1.125 mol/dm³
46.A burette reading is taken from the top of the meniscus. The bottom of the meniscus is at 23.4 cm³ and the top is at 23.7 cm³. What is the correct reading to the nearest 0.05 cm³?
Medium
- A23.4 cm³
- B25.7 cm³
- C28 cm³
- D21.1 cm³
47.In a titration, 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide solution is neutralised by 22.5 cm³ of hydrochloric acid. Calculate the concentration of the hydrochloric acid in mol/dm³.
Medium
- A0.111 mol/dm³
- B-0.889 mol/dm³
- C1.111 mol/dm³
- D2.111 mol/dm³
48.A stopwatch display shows 2:30 (minutes:seconds). What is the time in seconds?
Easy
- A150 s
- B165 s
- C135 s
- D180 s

Cartes mémo

What is the most accurate way to measure a variable volume of liquid between 0 cm³ and 50 cm³?

A burette.

What is the most accurate way to measure a fixed volume of liquid?

A volumetric pipette.

When using a burette, from where should the volume be read?

From the bottom of the meniscus, with the eye level with the meniscus.

What is the typical precision of a laboratory thermometer?

Half or one degree Celsius.

What is the typical precision of a digital temperature probe?

0.1 °C.

What is the unit of mass most often used in chemistry?

Grams (g).

What should you do to a digital balance before use?

Tare (set to zero) it.

Name two methods for measuring the volume of a gas produced in a reaction.

Using a gas syringe or by downward displacement of water.

Which method for measuring gas volume is more precise?

A gas syringe.

What is a limitation of the downward displacement of water method for collecting gas?

It does not work if the gas is soluble in water.

Define 'solute'.

The substance which dissolves in a liquid to form a solution.

Define 'solvent'.

The liquid in which a solute dissolves.

Define 'saturated solution'.

A solution with the maximum concentration of solute dissolved in the solvent at a given temperature.

Define 'filtrate'.

The liquid or solution that has passed through a filter.

Define 'residue'.

The substance that remains after evaporation, distillation, filtration or any other similar process.

What is the purpose of a titration?

To determine the concentration of a solution by reacting it with a solution of known concentration.

What indicator is suitable for a strong acid-strong base titration?

Methyl orange or phenolphthalein.

What colour is phenolphthalein in alkali?

Pink.

What colour is methyl orange in acid?

Red.

What is the endpoint of a titration?

The point where one drop causes a sharp colour change in the indicator.

What are concordant results in a titration?

Two results that are within 0.1 cm³ of each other.

Why should the funnel be removed from the burette during a titration?

To prevent liquid dripping into the burette and causing false/high readings.

What is the jet space of a burette?

The part of the burette after the tap.

Why is it important to fill the jet space of a burette before starting a titration?

To avoid false readings.

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