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# C2 help - Chemistry AQA GCSE watch

1. 2 questions from the textbook that I'm really stuck on...
1. A sample of a compound contains 3.9g of Potassium, 1.2g of Carbon, and 1.4g of nitrogen. What is its formula?

(I keep on getting really large numbers)

2. A compound is made up of 27% sodium by mass, 16% nitrogen by mass, and 56% oxygen by mass. What is its formula?

Thanks!
2. (Original post by JenniMusic)
2 questions from the textbook that I'm really stuck on...
1. A sample of a compound contains 3.9g of Potassium, 1.2g of Carbon, and 1.4g of nitrogen. What is its formula?

(I keep on getting really large numbers)

2. A compound is made up of 27% sodium by mass, 16% nitrogen by mass, and 56% oxygen by mass. What is its formula?

Thanks!
To do this type of question you must divide the percentages by their relative masses then divide through by the smallest number.

If this does not give you integers you have to either divide or multiply all by a suitable number which will give you all integers.
3. (Original post by charco)
To do this type of question you must divide the percentages by their relative masses then divide through by the smallest number.

If this does not give you integers you have to either divide or multiply all by a suitable number which will give you all integers.
I've tried that, but the integers are really large (over 200), and all of the other questions in this section I've done have much smaller integers (2, 4)
4. A sample of a compound contains 3.9g of Potassium, 1.2g of Carbon, and 1.4g of nitrogen. What is its formula

K
3.9/39 = 0.1

C
1.2/12 = 0.1

N
1.4/14 = 0.1

Therefore ratio is 11

formula is KCN
5. A compound is made up of 27% sodium by mass, 16% nitrogen by mass, and 56% oxygen by mass. What is its formula

Na:
27/23 = 1.17

N:
16/14 = 1.14

O:
56/16 = 3.5

Divide by smallest number:

ratio is: 1 3

therefore formula is NANO3

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