Question Video: Determining the Equation to Calculate Percentage Purity | Nagwa Question Video: Determining the Equation to Calculate Percentage Purity | Nagwa

# Question Video: Determining the Equation to Calculate Percentage Purity Chemistry • Third Year of Secondary School

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What is the equation that gives percentage purity in terms of the mass of the pure chemical and the mass of the sample?

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### Video Transcript

What is the equation that gives percentage purity in terms of the mass of the pure chemical and the mass of the sample?

To help us understand this question, let’s consider two beakers. The beaker on the left only contains water, so this sample is a pure substance. The beaker on the right however contains sodium chloride and water, a mixture of two different substances. So the sample is impure. We can quantify how pure a substance is with purity, a measure of the extent to which a substance is free from impurities.

To answer the question, we need to determine an equation that gives the percentage purity. As we are told that purity is a percentage, let’s consider how a standard percentage is calculated. To find a percentage, we divide the part in question by the whole then multiply by 100 percent. So, for example, if we wanted to know what percentage of the dots is pink, we would divide three, the number of pink dots, by 10, the total number of dots, then multiply by 100 percent.

When determining purity, we want to know what percentage of a sample is pure. This means that the part must be the amount of pure chemical and the whole must be the amount of sample.

Using what we know about percentages and the terms mass of the pure chemical and mass of the sample, we can construct an equation for percentage purity. Percentage purity equals the mass of the pure chemical divided by the mass of the sample times 100 percent. Using this equation, we can see that a pure sample has a percentage purity of 100 percent, while an impure sample has a percentage purity of less than 100 percent.

In conclusion, the equation that gives percentage purity is percentage purity equals mass of pure chemical divided by mass of sample times 100 percent.

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