Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.
What to Focus On
Core idea:Solvent asks what the sample is, what property is being used, and whether a new substance is formed.
Common stuck point:Students often know a formula related to solvent but skip the recognition step: Am I classifying matter or using properties, state, particle behavior, or mixture evidence to describe a sample? That leads to a correct-looking substitution attached to the wrong chemical model.
Sense of Study hint:Ask: Am I classifying matter or using properties, state, particle behavior, or mixture evidence to describe a sample?
Worked Examples
Example 1
easy
Why is water called the 'universal solvent'?
Answer
Water’s polarity allows it to dissolve many ionic and polar substances.
First step
1
Water is polar — the O–H bonds create a molecule with a partial negative end (O) and partial positive end (H).
Full solution
2
This polarity allows water to dissolve many ionic compounds (by attracting ions) and polar molecules.
3
No other common solvent dissolves as many different substances as water.
The term 'universal solvent' is an exaggeration — water does not dissolve everything (e.g., oil is nonpolar and does not dissolve well in water). The principle 'like dissolves like' governs solubility.
Example 2
medium
Explain 'like dissolves like' using the example of oil and water versus oil and hexane.
Example 3
medium
A bottle contains 80g ethanol and 20g water. Identify the solvent and find its mass percent of the solution.
Example 4
hard
You have 0.40L of 1.5M HCl. What volume of solvent (water) must you add to reduce concentration to 0.30M?
Example 5
hard
In 250g of 30.0% KCl solution, what is the mass of solvent (water)?
Example 6
challenge
A laboratory needs to prepare 2.00L of 0.150M NaOH (M=40.00g/mol) using solid NaOH and water. Describe the procedure including the role of water as the solvent.
Practice Problems
Try these problems on your own first, then open the solution to compare your method.
Example 1
easy
In a solution of ethanol and water where water is 70% by volume, which is the solvent?
Example 2
hard
Nail polish does not dissolve in water but dissolves easily in acetone. Explain why a different solvent is needed, and predict whether nail polish would dissolve in vegetable oil.
Example 3
easy
In salt water, which component is the solvent?Salt water: two particle types dissolved in one liquid phase
Example 4
easy
In sugar dissolved in tea, what is the solvent?
Example 5
easy
Why is water called the 'universal solvent'?
Example 6
easy
In a copper-zinc alloy that is mostly copper, which is the solvent?
Example 7
easy
Nail polish remover dissolves polish using acetone. What is the solvent?
Example 8
easy
In air (mostly nitrogen with other gases), which gas acts as the solvent?
Example 9
easy
In a sugar-water solution, which component is present in the larger amount?
Example 10
easy
Oil-based paints use a solvent like turpentine. What is the solvent?
Example 11
medium
In a mixture of 90 g water and 10 g salt, identify the solvent and justify with the amount criterion.
Example 12
medium
In a mixture of 95 g ethanol and 5 g water, which is the solvent? Explain why it is not water.
Example 13
medium
Why does oil (nonpolar) fail to dissolve in water (polar)? State the rule that governs this.
Example 14
medium
A chemist needs to dissolve a nonpolar wax. Should they choose water or hexane as the solvent, and why?
Example 15
medium
In brass (mostly copper), explain why copper is the solvent and what kind of solution this forms.Brass: a solid solution where copper (solvent) and zinc (solute) atoms share a lattice
Example 16
medium
Dry-cleaning uses a nonpolar solvent instead of water. Why is this an advantage for greasy stains?
Example 17
medium
Sugar dissolves faster in hot tea than iced tea. What role does the solvent's temperature play?
Example 18
challenge
A solution is 80 g water + 20 g salt. Identify the solvent, compute the solvent's mass percent, and interpret it.
Example 19
challenge
Explain, using molecular polarity, why water dissolves NaCl but not candle wax, naming the role water plays in each case.
Example 20
challenge
In a 60 g acetone + 40 g water mixture used to clean a surface, identify the solvent, and explain how the answer would change if amounts were reversed.
Example 21
medium
More sugar dissolves in hot water than in cold water. What does this say about the solvent's temperature and its capacity?
Example 22
medium
A grease stain resists water but lifts with dish soap. Explain the solvent-related role soap plays.
Example 23
easy
In sugar water, which substance is the solvent?
Example 24
easy
In air, the major gas is nitrogen (78%) with oxygen, argon, CO2 dissolved in it. What is the solvent?
Example 25
easy
In gasoline, additives are dissolved in a hydrocarbon mixture. What is the solvent?
Example 26
easy
In a 90% ethanol / 10% water solution, what is the solvent?
Example 27
easy
A polish remover smells of acetone and removes nail polish. What does this say about acetone's role?
Example 28
medium
A perfume contains essential oils dissolved in ethanol. Identify the solvent and explain why water is a poor substitute.
Example 29
medium
A mechanic uses kerosene to clean a greasy engine part. Why is kerosene a better solvent than water for grease?
Example 30
medium
A chemist uses hexane to dissolve a triglyceride. Predict whether the same substance would dissolve in water, and explain why.
Example 31
medium
In 14-karat gold (∼58% Au, rest Cu/Ag), what is the solvent and the resulting state of matter?14-karat gold: a solid solution with Au as the solvent and Cu/Ag as solutes
Example 32
medium
Why does stirring or heating water (the solvent) increase the dissolving rate of sugar?
Example 33
medium
100mL of 0.40M NaCl is diluted by adding 300mL water (the solvent). What is the new concentration?
Example 34
medium
A nurse needs 500mL of 0.50M glucose. How many mL of 2.0M stock and how many mL of water (solvent) are needed?
Example 35
hard
A solution of I2 in CCl4 shows a violet color. The same I2 does NOT noticeably dissolve in water. Identify the solvents and explain.
Example 36
hard
A chemist mixes 50mL of 0.20M NaCl with 150mL of 0.10M NaCl. Water acts as the common solvent. Find the final NaCl concentration.
Example 37
hard
Vegetable oil and vinegar (mostly water) do not mix. Identify the two possible solvents and explain the immiscibility in polarity terms.
Example 38
hard
Soap molecules have a polar 'head' and a nonpolar 'tail'. Explain how soap allows water (polar solvent) to remove a greasy stain.
Example 39
hard
A chemist wants to dissolve sodium chloride in liquid ammonia (NH3). Predict whether NH3 will be a good solvent for NaCl, and justify.
Example 40
challenge
A 'green' chemist replaces dichloromethane with ethanol as the solvent for an extraction. State two practical reasons this can work, and one chemical caveat.