How do you read a solubility curve, and what makes a solution saturated, unsaturated or supersaturated?
Solutions and solubility curves: classify solutions as unsaturated, saturated or supersaturated, and use the Table G solubility curves to determine how much solute dissolves at a given temperature.
A focused Regents Chemistry answer on solutions and the Table G solubility curves: solute and solvent, saturated, unsaturated and supersaturated solutions, the factors that affect solubility, and how to read grams of solute per 100 g of water from the curve.
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What this topic is asking
The Core Curriculum asks you to describe solutions, classify them as unsaturated, saturated or supersaturated, and use the Table G solubility curves to find how much solute dissolves at a given temperature. Reading Table G is one of the most common Part B-2 graph tasks on the Regents.
Solute, solvent and solution
Because a solution is homogeneous, every sample of it has the same composition, unlike a heterogeneous mixture. Dissolving is faster when the solute is in smaller pieces, the mixture is stirred, or (for solids) the temperature is higher, because these increase the contact and motion between particles.
Saturated, unsaturated and supersaturated
The values on Table G are the saturation amounts. Comparing a stated mass of solute to the curve tells you which category a solution is in: below the curve is unsaturated, on the curve is saturated, above the curve is supersaturated.
Reading Table G
The Table G curves plot grams of solute per 100 g of water against temperature in degrees Celsius. To find the maximum solubility at a temperature: find the temperature on the horizontal axis, go up to the curve for that solute, and read across to the vertical axis. To decide how much solute will crystallize when a saturated solution is cooled, find the solubility at the higher and lower temperatures and subtract.
Try this
Q1. State what type of mixture a solution is. [1 point]
- Cue. A homogeneous mixture (uniform composition throughout).
Q2. Using the Table G trend, state how the solubility of a gas in water changes as temperature rises. [1 point]
- Cue. It decreases (gas solubility falls as temperature increases).
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (Part B-2 style)3 marksUsing the Table G solubility curve for potassium nitrate, : (a) determine the mass of that dissolves in g of water at to form a saturated solution; (b) state whether a solution containing g of in g of water at is saturated, unsaturated or supersaturated; (c) describe how to make a supersaturated solution.Show worked answer →
A 3-point constructed-response item reading the Table G curve.
(a) Saturation mass (1 point): reading the curve at gives about g per g of water (accept a close value).
(b) Classification (1 point): g is below the saturation value (about g) at that temperature, so the solution is unsaturated (more could dissolve).
(c) Supersaturated solution (1 point): dissolve as much solute as possible at a high temperature to make a saturated solution, then cool it slowly and carefully so the excess solute stays dissolved.
Markers reward reading the curve value, comparing the given mass to it, and describing the heat-then-cool method for a supersaturated solution.
Regents (Part A style)1 marksAs the temperature increases, the solubility of most solid solutes in water (1) increases (2) decreases (3) remains the same (4) becomes zeroShow worked answer →
A 1-point Part A item on the Table G trend. The answer is (1) increases.
For most solid solutes the solubility curves on Table G slope upward, meaning more solute dissolves at higher temperatures. (Gases are the exception: gas solubility decreases as temperature increases.) The upward slopes are why heating then cooling a saturated solution can produce a supersaturated solution.
Markers reward recognizing that the solubility of most solids increases with temperature, as the Table G curves show.
Related dot points
- Concentration and molarity: calculate molarity, parts per million and percent by mass using the concentration formulas on Table T.
A focused Regents Chemistry answer on solution concentration: molarity as moles of solute per liter of solution, parts per million, and percent by mass, all from the Table T formulas, with worked calculations and the dilution idea.
- States of matter and kinetic molecular theory: describe the particle arrangement and energy in solids, liquids and gases, and state the assumptions of the kinetic molecular theory of an ideal gas.
A focused Regents Chemistry answer on the three states of matter and kinetic molecular theory: how particle arrangement and motion differ across solids, liquids and gases, the assumptions of an ideal gas, and how real gases deviate from ideal behavior.
- Heating and cooling curves: interpret heating and cooling curves, distinguishing changes in kinetic energy from changes in potential energy during phase changes.
A focused Regents Chemistry answer on heating and cooling curves: why temperature is constant during a phase change, how kinetic and potential energy change in each segment, and how to read melting and boiling plateaus from the graph.
- Properties of ionic, molecular and metallic substances: relate melting point, electrical conductivity, hardness and solubility to the type of bonding and structure.
A focused Regents Chemistry answer on how bonding type explains properties: why ionic solids have high melting points and conduct only when molten or dissolved, why molecular substances are soft and low-melting, and why metals conduct and are malleable.
- Heat and calorimetry: calculate heat changes using q = mC(delta-T) for temperature changes and q = mH for phase changes, with constants from Table B and formulas from Table T.
A focused Regents Chemistry answer on heat and calorimetry: the q = mC(delta-T) equation for warming or cooling, q = mH for melting and boiling, the water constants on Table B, and the difference between exothermic and endothermic changes.
Sources & how we know this
- Physical Setting/Chemistry Core Curriculum — New York State Education Department (2002)
- Reference Tables for Physical Setting/Chemistry, 2011 Edition — New York State Education Department (2011)