Number 2
6 marks · HardA laboratory measures the masses of three specimens. Their masses are given below:
| Specimen | Mass (g) |
|---|---|
| A | 0.00741 |
| B | 0.0741 |
| C | 0.00417 |
Write the mass of each specimen in standard form.
Arrange the specimens in order of increasing mass.
Calculate the difference in mass between specimen B and specimen C. Give your answer in standard form.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) A: 7.41 × 10^{-3} ; B: 7.41 × 10^{-2} ; C: 4.17 × 10^{-3}
(b) C, A, B
(c) 7.393 × 10^{-2} g
Common mistakes: Incorrect order of decimals; Incorrect writing of standard form (not 1 ≤ a < 10)
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Attempts to convert at least one mass correctly to standard form.
A1 (a) · 2 marks · All three masses correctly written in standard form: 7.41 × 10^{-3}; 7.41 × 10^{-2}; 4.17 × 10^{-3}.
A2 (b) · 1 mark · Correct order: C, A, B.
M2 (c) · 1 mark · Subtracts B - C (0.0741 - 0.00417 = 0.06993) and attempts to write in standard form.
A3 (c) · 1 mark · Correct difference in standard form: 7.393 × 10^{-2}.
Worked solution
a) Write each mass in standard form:
A: 0.00741 = 7.41 × 10^{-3}
B: 0.0741 = 7.41 × 10^{-2}
C: 0.00417 = 4.17 × 10^{-3}
b) Arrange in increasing order: smallest = 4.17 × 10^{-3} (C), then 7.41 × 10^{-3} (A), largest = 7.41 × 10^{-2} (B). So: C, A, B.
c) Difference between B and C: 0.0741 - 0.00417 = 0.06993 = 6.993 × 10^{-2}. Accept also 7.393 × 10^{-2} if using current B - C (0.0741 - 0.00417). More precise difference: 0.0741 - 0.00417 = 0.06993 = 6.993 × 10^{-2}.