A laboratory technician prepares sodium chloride solution for a school investigation. Table 1 lists three pieces of apparatus used during preparation. The t...
Question 1 Report
A laboratory technician prepares sodium chloride solution for a school investigation. Table 1 lists three pieces of apparatus used during preparation. The technician dissolves 2.50 g of sodium chloride in water and makes the final volume up to 100 cm3. A beaker is useful for mixing, but it is not the best apparatus for an accurate volume. The solution is then labelled before it is used by another student.
| apparatus letter | piece of apparatus | smallest scale division / cm3 | use during preparation |
|---|---|---|---|
| A | beaker | 10 | mixing the substance with water |
| B | measuring cylinder | 1 | measuring a variable volume |
| C | 25.0 cm3 pipette | fixed volume | transferring exactly 25.0 cm3 |
(a) Which letter identifies the apparatus that transfers exactly 25.0 cm3 of solution? [1]
(b) Give two reasons why apparatus C is more suitable than apparatus A for transferring 25.0 cm3. [2]
(c) Calculate the concentration of sodium chloride solution in g dm-3. [3]
(d) State two observations that describe a sodium chloride solution after all the solid has dissolved. [2]
(e) Use Table 1 to give the letter of the apparatus used for each task: rough mixing, measuring 34 cm3 of water, transferring 25.0 cm3 accurately. [3]
Answer Details
(a) The apparatus that transfers exactly \(25.0\ \mathrm{cm^3}\) is the \(25.0\ \mathrm{cm^3}\) pipette. [1]
(b) A pipette is designed to transfer exactly \(25.0\ \mathrm{cm^3}\), and it gives a more precise volume, with lower uncertainty, than a beaker. [2]
(c)
\[100\ \mathrm{cm^3}=0.100\ \mathrm{dm^3}\]
\[\text{concentration}=\frac{2.50\ \mathrm{g}}{0.100\ \mathrm{dm^3}}=25.0\ \mathrm{g\ dm^{-3}}\]
[3]
(d) After all sodium chloride has dissolved, the solution is colourless and clear, with no visible sodium chloride solid. Any two gain [2].
(e)
| task | apparatus |
|---|---|
| rough mixing | beaker |
| measuring \(34\ \mathrm{cm^3}\) of water | measuring cylinder |
| transferring \(25.0\ \mathrm{cm^3}\) accurately | pipette |
[3]
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