Chemistry Solutions and Molarity Quiz

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Questions and Answers

What is the definition of concentration in the context of solutions?

Concentration is the amount of solute per unit volume of solution.

How is molarity defined?

Molarity (M) is defined as the number of moles of a chemical substance present in 1 L of solution.

What is the molarity of a 3 M hydrochloric acid solution?

[HCl] = 3 mol L-1.

How many moles of NaCl are present in 100 mL of a 2 M solution?

0.2 moles of NaCl. Signup and view all the answers

To prepare 500 mL of a 1 M NaCl solution, how many moles of NaCl are needed?

0.5 moles of NaCl. Signup and view all the answers

What is the formula to calculate the mass of NaCl required to make a 0.5 mole solution?

0.5 moles × 58.5 g mol-1. Signup and view all the answers

What is the molar mass of NaCl?

58.5 g mol-1. Signup and view all the answers

If you have a 2 M solution, how many moles are there in 1 L?

2 moles. Signup and view all the answers

What does one mole of a substance represent in terms of particles?

One mole of a substance represents Avogadro's number of particles, which is approximately $6 \times 10^{23}$ particles. Signup and view all the answers

How do you calculate the molar mass of a compound?

The molar mass of a compound is calculated by summing the molar masses of each atom multiplied by the number of atoms of that element in the compound. Signup and view all the answers

What is the molar mass of glucose, C6H12O6?

The molar mass of glucose, C6H12O6, is 180 g/mol. Signup and view all the answers

If you have 540 g of glucose, how many moles do you have?

You have 3 moles of glucose in 540 g. Signup and view all the answers

What is the difference between a solvent and a solute in a solution?

The solvent is the substance present in the largest amount, while the solute is the substance that dissolves in the solvent. Signup and view all the answers

Define a solution in terms of its composition.

A solution is a homogenous mixture of two or more substances. Signup and view all the answers

What is the significance of solubility in the context of solutions?

Solubility indicates how well a substance can dissolve in a particular solvent. Signup and view all the answers

How is the amount of solute quantified in a solution?

The amount of solute is quantified in moles, which relates to the mass of the solute and its molar mass. Signup and view all the answers

What is the final concentration of HCl when 100 mL of a 2 M solution is diluted to 1 L?

0.2 M Signup and view all the answers

Why is it often impractical to dilute a solution in one go, such as from 10 mL to 500 L?

It requires extremely large volumes that can be difficult to measure accurately. Signup and view all the answers

When performing a serial dilution with a stock concentration of 2 M, what is the concentration after the first dilution step using 1 mL of solution to 9 mL of solvent?

0.2 M Signup and view all the answers

Explain what happens to the concentration during each step of a serial dilution.

The concentration is reduced progressively, typically by a consistent dilution factor. Signup and view all the answers

If an initial solution of concentration 2 M is diluted four times using the same volumes, what is the final concentration after all dilutions?

0.02 M Signup and view all the answers

What is the mathematical relationship used to derive the final concentration after dilution?

C_initial × V_initial = C_final × V_final Signup and view all the answers

After a 1:10 dilution, how much less concentrated is the final solution compared to the stock solution?

10 times less concentrated Signup and view all the answers

How does a serial dilution help in achieving very low concentrations from a high concentration stock solution?

By repeatedly diluting in smaller, manageable steps. Signup and view all the answers

How would you calculate the mass of agar needed for a 1.5% w/v nutrient agar solution in 250 mL?

You would calculate 1.5% of 250 mL, which is 3.75 g of agar needed. Signup and view all the answers

What is the concentration in mol/L of a solution made by dissolving 2 moles of glucose in 500 mL of water?

The concentration is 4 mol/L or 4 M. Signup and view all the answers

What does it mean to dilute a solution with respect to solute amount?

Diluting a solution means the amount of solute remains the same, but the concentration decreases. Signup and view all the answers

State the dilution formula used to find the concentration after dilution.

The dilution formula is Cinit × Vinit = Cfinal × Vfinal. Signup and view all the answers

How do you find the concentration of diluted HCl after combining 100 mL of 2 M solution with 900 mL of water?

You find the concentration using Cfinal = (Cinit × Vinit) / Vfinal, which results in 0.2 M. Signup and view all the answers

In the context of preparing a solution, what does a stock solution refer to?

A stock solution is a concentrated solution prepared in bulk and used to create lower concentration solutions. Signup and view all the answers

If you have a 250 mL solution and want to make it 1.5% w/v, how many grams of solute is required?

You would need 3.75 g of solute for the 250 mL solution. Signup and view all the answers

What happens to the moles of solute before and after dilution?

The moles of solute remain unchanged during the dilution process. Signup and view all the answers

What is the concentration of the new solution after diluting 1 mL of a 0.2 mol L-1 solution to 10 mL?

0.02 mol L-1 Signup and view all the answers

If the stock solution has a concentration of 2 mol L-1, what dilution factor is achieved after four serial dilutions?

1:10000 Signup and view all the answers

During a titration, what happens when the reaction between HCl and sodium carbonate reaches completion?

A color change occurs due to the indicator added, signaling the end of the reaction. Signup and view all the answers

Given 23.5 mL of 0.5 M HCl is used in a titration, how many moles of HCl are involved?

0.01175 moles Signup and view all the answers

What is the overall concentration change from the original 2 M solution to the final solution after four serial dilutions?

10000 times less concentrated Signup and view all the answers

How can we determine the concentration of sodium carbonate in the titration if we know the concentration of HCl?

By using the stoichiometry of the balanced chemical equation and the known moles of HCl. Signup and view all the answers

What is the final concentration of a solution if a 0.002 mol L-1 solution is diluted to 10 mL from 1 mL?

0.0002 mol L-1 Signup and view all the answers

What is the concentration of the sodium carbonate solution after the reaction with HCl is complete?

0.05 M Signup and view all the answers

Study Notes

General Chemistry: Concentration and Molarity

Lecture Topics: The Mole, Concentrations, Changing Concentration (Dilutions), Titration Calculations

The Mole

Atomic Mass: 1 hydrogen atom = 1 Da (or 1 a.m.u.)
Molecular Mass: 1 H₂O molecule = 18 Da (2 × 1 Da + 1 × 16 Da)
Molar Mass: The mass of one mole of a substance in grams, listed on the periodic table.
Avogadro's Number: 6 × 10²³ particles per mole
Mole Calculation Examples:
- 1 mole of Hydrogen = 6 × 10²³ atoms = 1 g [molar mass = 1 g/mol]
- 1 mole of H₂O = 6 × 10²³ molecules = 18 g [molar mass = 18 g/mol]
Molar Mass of a Compound: The sum of the molar masses of each atom in the compound.
- Glucose (C₆H₁₂O₆): (6 × 12 g/mol) + (12 × 1 g/mol) + (6 × 16 g/mol) = 180 g/mol
- Calculating Amount (in moles) of Glucose (540 g Sample): 540 g / 180 g/mol = 3 moles

Concentrations

Solution: Homogenous mixture of two or more substances.
Solvent: Substance present in the largest amount (moles).
Solute: Other substances present in the solution.
Solubility: Ability of a substance to dissolve in a particular solvent.
Concentration: Amount of solute per unit volume of solution. Molarity (M) is the number of moles of a chemical substance in 1 L of solution.
- 3 M solution of HCl (Hydrochloric Acid) => [HCl] = 3 mol L⁻¹

Calculating Amount of Solute in a Sample

Example 3: 100 mL (0.1 L) of 2 M NaCl solution => 0.2 moles of NaCl.

Preparing Solutions

Example 4: Preparing 500mL of 1 M NaCl solution requires 0.5 moles of NaCl, which is equal to 29.25 g.
Volumetric Flasks: Used for preparing solutions of known concentration.

% Weight/Volume (w/v %)

Example 5: 1.5% w/v nutrient agar solution for 250mL: 3.75 g of agar required.

Calculating Solution Concentration

Example 6: 2 moles of glucose in 500mL solution => 4 M (4 mol L⁻¹)

Changing the Concentration: Dilutions

Diluting a Solution: Amount of solute remains constant; concentration decreases.
Formula: CᵢVᵢ = CₓVₓ (initial concentration × initial volume = final concentration × final volume)
- Example 7: 100 mL of 2 M HCl diluted to 1 L => 0.2 M HCl
Intuitive Approach (Example 7): Diluting 100 mL of 2 M solution to 1000 mL divides the concentration by 10 => 0.2 M

Serial Dilutions

Serial Dilutions: A series of dilutions to significantly reduce the concentration of a solution.
Example 8: Stock solution (2 M), taking 1 mL and adding it to 9 mL solvent, 3 more similar steps = 0.0002 M

Titrations

Titrations: Measure concentration by reacting one solution with another of known concentration.
Reaction: A + B → C (e.g., 2HCl + Na₂CO₃ → 2NaCl + CO₂ + H₂O)
Indicator: Changes colour to indicate completion of reaction.
Example 9: Calculating sodium carbonate (Na₂CO₃) concentration in a reaction with known HCl concentration.

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Description

Test your knowledge on key concepts related to solutions, including molarity, solutes, and solvents. This quiz covers definitions, calculations, and the significance of solubility in chemistry. Perfect for students studying general chemistry and solution concentrations.