Calculate the concentration of a solution when of sodium chloride is dissolved in of water. Give your answer to an appropriate number of significant figures.
Step 1: Identify the values and their significant figures.
Step 2: Convert the volume to .
Step 3: State the formula and substitute the values.
Step 4: Calculate and round the final answer.
Students often round intermediate values during a multi-step calculation. Keep the full unrounded value in your calculator to avoid "premature rounding" errors that will cost you the final accuracy mark.
When the command word 'Calculate' is paired with 'an appropriate number of significant figures', examiners expect you to apply the 'least significant data' rule to your final answer.
In OCR chemistry, whole numbers ending in zero (like 500) can be ambiguous; always follow the 'least significant data' rule based on the other values provided in the question.
For titration practicals, examiners expect your burette readings to be recorded to exactly two decimal places, ending in either a .00 or a .05.
Significant figures
The digits in a number that carry meaning contributing to its measurement resolution or precision, starting from the first non-zero digit.
Raw data
The original measurement values provided in an exam question used to perform a calculation.
Appropriate number of significant figures
A degree of precision in a calculated answer that matches the precision of the least accurate piece of input data.
Least significant data
The piece of data in a calculation that has the lowest number of significant figures, which subsequently limits the precision of the final result.
Rounding
The process of reducing the digits in a number while keeping its value similar.
Resolution
The smallest change in the quantity being measured that causes a perceptible change in the reading of the measuring instrument.
Put your knowledge into practice — try past paper questions for Chemistry A
Significant figures
The digits in a number that carry meaning contributing to its measurement resolution or precision, starting from the first non-zero digit.
Raw data
The original measurement values provided in an exam question used to perform a calculation.
Appropriate number of significant figures
A degree of precision in a calculated answer that matches the precision of the least accurate piece of input data.
Least significant data
The piece of data in a calculation that has the lowest number of significant figures, which subsequently limits the precision of the final result.
Rounding
The process of reducing the digits in a number while keeping its value similar.
Resolution
The smallest change in the quantity being measured that causes a perceptible change in the reading of the measuring instrument.