Chapter 5 Test: Mixtures...And How To Separate Them

Which characteristic property let us separate a mixture of isopropanol and water?

• Melting point

• Density

• Boiling point

• Freezing point

• Solubility

Characteristic properties of substances are useful for all of the following reasons except:

• They can help separate mixtures.

• They can help identify pure substances.

• They can tell you how much of the substance you have.

Potassium nitrate and sodium chloride are both white, crystallized solids at room temperature.  Their melting points are too high for our burners to melt them, and the crystals are tiny and impossible to pick out by hand.  They have similar solubilities in water at room temperature as well, close to 40g/cm--and their densities are quite similar as well.  With all of this said, how could you actually separate these two substances from each other?

• Freeze them

• Dissolve them both in hot water and filter it; repeat to get them more purely separated

• Put them in water and see which one dissolves first

• Put them in water and see which one floats; skim it off the top

The following substances are all acquired from crude oil.  If we were trying to separate a mixture of these by freezing them, which would turn into a solid first? Substance Melting Point (C) Boiling Point (C) Ethane -183 -88 Pentane -129 36 Hexane -94 69 Decane -30 174

• Ethane

• Pentane

• Hexane

• Decane

You have a pile of sawdust with tiny bits of nails mixed in it.  You want to compost the sawdust, but obviously not the metal bits.  Which characteristic property could you take advantage of to separate the metal from the sawdust in this mixture?

• Melting point

• Freezing point

• Boiling point

• Density

• Solubility

Which characteristic property allowed us to separate the pigments found in ink?

• Melting point

• Density

• Boiling point

• Solubility

• Freezing point

• Flammability

Which of the following is a pure substance and NOT a mixture?

• The dirt under your feet

• The blood in your veins

• The seawater in the Atlantic Ocean

• The isopropanol in rubbing alcohol

Isopropanol is flammable, doesn't dissolve sugar, and has a density of 0.80g/cm.  Water, of course, does not burn, does dissolve sugar, and has a density of 1.00g/cm.  If you mixed 100mL of water and 10mL of isopropanol together, which of the following statements would you expect to be false?

• The mixture might burn a little bit.

• The mixture would probably dissolve sugar fairly well.

• The total volume of the mixture would be about 110mL.

• The density of the mixture would be 0.90g/cm^3.

• If given time, the isopropanol would float to the top of the mixture.

Be as specific as possible and answer in complete sentences.

For questions 10-12: A thousand gallons of petroleum (crude oil) are removed from the ground and fractionally distilled.  The boiling points of some of the substances in petroleum are listed in the table below.  A graph of the temperature of the vapor above the liquid as a function of time appears below the table. Substance Boiling Point (C) 1 70 2 98 3 125 4 151 Which substance or substances will be collected during time interval IV?

For questions 10-12: A thousand gallons of petroleum (crude oil) are removed from the ground and fractionally distilled.  The boiling points of some of the substances in petroleum are listed in the table below.  A graph of the temperature of the vapor above the liquid as a function of time appears below the table. Substance Boiling Point (C) 1 70 2 98 3 125 4 151 Which substance or substances will still be present in the original liquid mixture at the beginning of time interval II?

For questions 10-12: A thousand gallons of petroleum (crude oil) are removed from the ground and fractionally distilled.  The boiling points of some of the substances in petroleum are listed in the table below.  A graph of the temperature of the vapor above the liquid as a function of time appears below the table. Substance Boiling Point (C) 1 70 2 98 3 125 4 151 During which time intervals would the substance collected definitely be a pure substance?

Suppose you try to separate a mixture of two solid substances by stirring the mixture with water, filtering, and evaporating the filtrate.  You do this and find nothing on the filter paper. a.  Explain why this procedure failed to separate the mixture, referring to a specific characteristic property. b.  What could you try next to separate the mixture?

By paper chromatography, you separate the solid dyes in black ink into three substances (blue, red, yellow).  You dissolve each substance in water, mix the solutions, and obtain a clear, purple solution.  Why is the solution lighter than the original ink?

This whole chapter has been about separating mixtures.  In a few sentences, explain as best you can why this is an idea worth understanding.  Use real world examples that we have discussed in class.  Think this through--answers like 'just because' or 'because we have to'--won't earn much credit here!

1.  Read all questions carefully and try to eliminate choices that are obviously wrong. 2.  If stuck on a question, skip it for now and come back later (don't forget to come back to it eventually) 3.  In essays, think before you write and be sure to answer the question that is asked. 4.  Please ask for clarification if something is unclear to you. 5. Take your time and do your best.  You will never regret doing the best you can.