8th Grade- Mixture, Compounds, and Pure Substances

Both mixtures and compounds are made of two or more different substances mixed together. So which of the following is an accurate statement about the difference between the two?

• Mixtures are made of more different substances

• Compounds are mixed physically but not chemically

• A mixture is two or more substances mixed physically but not chemically

• Compounds are easier to separate than mixtures

An atomic model of sulfuric acid (H2SO4) is shown. How many different elements have combined to form this compound of sulfuric acid?

• 2

• 3

• 6

• 7

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Which of the following is a pure substance?

• Orange Juice

• Lucky Charms Cereal

• Gold (Au)

• Granola and Yogurt Parfait

Salt has the chemical formula NaCl because it is made up of atoms of Sodium (Na) and Chlorine (Cl). Which statement most accurately describes this compound in relation to the elements it is made of?

• When sodium and chlorine chemically combine, they create a substance with completely different properties

• Salt has similar properties to the sodium and chlorine it is made of

• Once salt is formed the sodium and chlorine atoms no longer exist, only salt atoms

• Salt can easily be separated back into sodium and chlorine atoms through physical means

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Which of the following show a pure substance?

• a and b only

• a, b, c, and d

• a, b, and c

• a only

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Which of the following statements is true?

• All molecules are compounds but not all compounds are molecules

• All compounds are molecules but not all molecules are compounds

• All elements exist as molecules

• Any time two atoms combine a compound is formed

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You dissolve a white powder in a beaker of water. It is not likely that a chemical change took place if the water

• gets hotter

• remains clear

• starts to bubble

• turns orange

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This is a picture of

• Compound

• Elements

• Heterogenous solution

• Pure substance

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What is the only substance with a neutral pH of 7?

• Milk

• Pure Water

• Orange Juice

• Blood

A water molecule is made up of 2 hydrogen atoms and 1 oxygen atom. So the ratio for a water molecule is 2:1, hydrogen to oxygen. Which of the following statements is accurate concerning this ratio?

• If this ratio is changed slightly by adding or taking away one atom per molecule the resulting compound will still be water just with slightly different properties

• If this ratio is changed slightly by adding or taking away one atom per molecule the resulting compound will be something completely different with properties very different from water

• It is impossible to have a molecule with one less or one more atom

• Adding or taking away an atom from a water molecule is a physical change so the resulting compound will still have the same properties as water

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