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Lesson Worksheet: Determining Purity Chemistry

In this worksheet, we will practice determining the purity of a substance based on its proportion by mass and physical properties.

Q1:

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

  • APercentagepurity = massofsamplemassofpurechemicalmassofsample×100%.
  • BPercentagepurity = massofsamplemassofpurechemical×100%.
  • CPercentagepurity = massofpurechemicalmassofsample×100%.
  • DPercentagepurity = massofsamplemassofpurechemical.
  • EPercentagepurity = massofpurechemicalmassofsample.

Q2:

A mixture of nitrogen and oxygen gas has a mass of 1.20 kg. After 250 g of oxygen in the mixture is reacted with a metal, pure nitrogen is left behind. To 2 significant figures, what is the percentage purity of nitrogen in the original mixture?

Q3:

An impure sample of aluminum bromide contains 4%‎ contaminants by weight. What is the percentage purity of the sample?

Q4:

An impure sample of magnesium chloride has a mass of 50 g. After perfect purification, 45 g of magnesium chloride is recovered. What is the percentage purity of the original sample?

Q5:

Which of the following statements best describes what an impurity is?

  • AAn unwanted substance mixed within a desired substance
  • BA wanted substance mixed within a desired substance
  • CA substance finely dispersed in another substance
  • DA substance dissolved in another substance
  • EA substance that can be separated from another substance

Q6:

Which of the following is an effect that impurities do not typically have on the boiling or melting point of a substance?

  • AMaking the melting point occur over a larger temperature range
  • BDeviating from the reference value for the melting or boiling point
  • CMaking the boiling point occur sharply at a definite temperature
  • DIncreasing the boiling point
  • EDecreasing the melting point

Q7:

Which of the following substances can be considered chemically pure?

  • ABrass
  • BSeawater
  • CAir
  • DApple juice
  • EA bar of 24-karat gold

Q8:

A student obtains a sample of water and wants to test its purity by determining its melting and boiling points.

What results should the student expect to find if the sample is pure?

  • AThe sample boils at exactly 100C and freezes at exactly 0C.
  • BThe sample boils between 99C and 101C and freezes between 1C and 1C.
  • CThe sample boils and freezes over a large temperature range.
  • DThe sample boils over a large temperature range but freezes at exactly 0C.

How can the student obtain pure water if the sample is found to contain soluble impurities?

  • AFiltration
  • BTitration
  • CDistillation
  • DCrystallization

Q9:

The image below shows a labeled bottle of orange juice.

Why might the company claim the orange juice is 100% pure?

  • AIt has a pH of 7, making it neutral.
  • BIt contains no added or artificial products.
  • CIt is made up of any one type of compound.
  • DThe solution is completely orange in color.
  • EThe oranges were organically grown.

Why might a chemist say the orange juice is not pure?

  • AIt only contains an artificial substance.
  • BThe particles are free to move around each other.
  • CIt does not contain just one substance.
  • DIt is slightly acidic.
  • EThe solution is not colorless.

Q10:

5 g of salt is mixed with 20 g of powdered sugar. Which of the following statements best describes this mixture?

  • ASugar is considered an impurity, and its percentage is 80%.
  • BEither sugar or salt can be an impurity interchangeably.
  • CSalt is considered an impurity, and its percentage is 25%.
  • DSugar is considered an impurity, and its percentage is 75%.
  • ESalt is considered an impurity, and its percentage is 20%.

This lesson includes 17 additional questions and 4 additional question variations for subscribers.

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