A level chemistry core maths skills

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A level chemistry - standard form

In science, very large and very small numbers are usually written in standad form. Standard form is writing a number in the format A x 10* (asterisk is also x) where A is a number from 1 to 10 and *(X) is the number of places you move the decimal place.

For example, to express a large number such as 50,000 mol dm-3 (to the power of 3) in standard form, A = 5 and x = 4 as there are four numbers after the initial 5. 

Therefore, it would be written as 5 x 10(to the power of 4) mol dm(to the power of -3).

To give a small number such as 0.00002 Nm(to the power of 2) in standard form, A = 2 and there are five numbers before it so x = -5.

So it is written as 2 x 10(to the power of -5) Nm(to the power of 2).

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A level chemistry - significant figures & decimal

In chemistry, you are often asked to express numbers to either three or four significant figures. The word significant means to 'have meaning'. A number that is expressed in significant figures will only have digits that are imporatnt to the number's precision.

It is important to record your data and your answers to calculations to a reasonable number of significant figures. Too many and your answer is claiming an accuracy that it does not have, too few and you're not showing precision and care required in scientific analysis.

For example, 6.9301 becomes 6.93 if written to three significant figures.

Likewise, 0.00043456 is 0.00043 to three significant figures.

Notice that the zeros before the figure are not significant - they just show you how large the number is by the position of the decimal point. Here, a 5 follows the last significant digit, so just s with decimals, it must be rounded up.

Any zeros between the other significant figures are significant. For example, 0.003018 is 0.00302 to three significant figures. 

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