Question

Some help on these questions would be awesome:

1) An 88 g sample of carbon dioxide is found to contain 24g of carbon and 64g of oxygen. What is the percentage by mass of all elements? Give answers to the nearest whole number.

3) A 57 g sample of sodium carbonate reportedly contains 25g of sodium, 18g of carbon and 20g of oxygen. Do you accept this analysis? Explain why or why not.

5) Pink gold contains 75% gold, 20% copper and 5% silver by mass. Determine the mass of each metal in a pink gold necklace that weighs 20g.

6a) Carbon monoxide is 43% carbon by mass; nitrous oxide is 30% nitrogen by mass. For both gases, the remainder is oxygen. In a mixture containing 5g of each gas, what is the mass of oxygen present?

6b) A 5g sample of carbon monoxide is mixed with 4g of nitrous oxide and 3 g of sulfur dioxide. Sulfur dioxide is 50% sulfur by mass, the balance is oxygen. What is the percentage by mass of oxygen and of sulfur present in the mixture? Use the mass compositions given in part a.​

Answer 1

To find the percentage by mass of each element, divide the mass of each element by the total mass of the sample and multiply by 100:
Carbon: 24 g / 88 g * 100% = 27.3% (rounded to 27%)
Oxygen: 64 g / 88 g * 100% = 72.7% (rounded to 73%)

So, the sample is 27% carbon and 73% oxygen by mass.

To determine whether the reported analysis is correct, we need to check if the masses of the elements add up to the total mass of the sample:
25 g + 18 g + 20 g = 63 g
57 g ≠ 63 g

Since the masses of the elements do not add up to the total mass, the reported analysis is not accepted.

To find the mass of each metal in the necklace, multiply the weight of the necklace by the percentage of each metal:
Gold: 20 g * 75% = 15 g
Copper: 20 g * 20% = 4 g
Silver: 20 g * 5% = 1 g

So, the necklace contains 15 g of gold, 4 g of copper, and 1 g of silver.

6a) To find the mass of oxygen present, subtract the mass of the other two elements from the total mass:

5 g + 5 g = 10 g
Total mass = 10 g
Mass of other elements = 43% * 5 g + 30% * 5 g = 2.15 g + 1.5 g = 3.65 g
Mass of oxygen = 10 g - 3.65 g = 6.35 g

So, there is 6.35 g of oxygen present in the mixture.

6b) To find the percentage by mass of each element, divide the mass of each element by the total mass of the mixture and multiply by 100:

Carbon monoxide: 5 g * 43% = 2.15 g
Nitrous oxide: 4 g * 30% = 1.2 g
Sulfur dioxide: 3 g * 50% = 1.5 g (balance is oxygen: 1.5 g * 100% / 50% = 3 g)
Total mass = 5 g + 4 g + 3 g = 12 g
Mass of other elements = 2.15 g + 1.2 g + 1.5 g + 3 g = 8.85 g
Percentage of oxygen = (12 g - 8.85 g) / 12 g * 100% = 26.25% (rounded to 26%)
Percentage of sulfur = 1.5 g / 12 g * 100% = 12.5%

So, the mixture contains 26% oxygen and 12.5% sulfur by mass