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Questions and Answers
A solution contains 3 moles of solute in 750 cm³ of solution. What is its concentration in mol/dm³?
A solution contains 3 moles of solute in 750 cm³ of solution. What is its concentration in mol/dm³?
In a titration, 20 cm³ of 0.2 mol/dm³ hydrochloric acid (HCl) neutralizes 25 cm³ of sodium hydroxide (NaOH). What is the concentration of the NaOH solution?
In a titration, 20 cm³ of 0.2 mol/dm³ hydrochloric acid (HCl) neutralizes 25 cm³ of sodium hydroxide (NaOH). What is the concentration of the NaOH solution?
A reaction has a theoretical yield of 15 grams, but the actual yield obtained is 12 grams. What is the percentage yield?
A reaction has a theoretical yield of 15 grams, but the actual yield obtained is 12 grams. What is the percentage yield?
In a reaction, the desired product has a Mr of 50 and the total Mr of all products is 100. What is the atom economy of this reaction?
In a reaction, the desired product has a Mr of 50 and the total Mr of all products is 100. What is the atom economy of this reaction?
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20 cm³ of an unknown concentration of potassium hydroxide (KOH) is titrated with 0.15 mol/dm³ hydrochloric acid (HCl). If 25 cm³ of HCl is needed to neutralise the KOH, what is the concentration of the potassium hydroxide solution?
20 cm³ of an unknown concentration of potassium hydroxide (KOH) is titrated with 0.15 mol/dm³ hydrochloric acid (HCl). If 25 cm³ of HCl is needed to neutralise the KOH, what is the concentration of the potassium hydroxide solution?
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What does one mole of a substance always contain?
What does one mole of a substance always contain?
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In a chemical reaction, what does the law of conservation of mass state?
In a chemical reaction, what does the law of conservation of mass state?
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In a reaction between 12g of magnesium and 20g of oxygen, what is the first step to determine the limiting reactant?
In a reaction between 12g of magnesium and 20g of oxygen, what is the first step to determine the limiting reactant?
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If 10g of hydrogen reacts with 32g of oxygen, how many moles of water, $H_2O$ can be formed? The molar mass of hydrogen is 1, oxygen is 16, and water is 18.
If 10g of hydrogen reacts with 32g of oxygen, how many moles of water, $H_2O$ can be formed? The molar mass of hydrogen is 1, oxygen is 16, and water is 18.
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What does it mean for a reactant to be the 'limiting reactant' in a chemical reaction?
What does it mean for a reactant to be the 'limiting reactant' in a chemical reaction?
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What is the concentration of a solution that contains 2 moles of solute in 500 cm³ of solution, in mol/dm³?
What is the concentration of a solution that contains 2 moles of solute in 500 cm³ of solution, in mol/dm³?
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Which of these is the correct formula to use when calculating number the of moles of a given substance?
Which of these is the correct formula to use when calculating number the of moles of a given substance?
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If a solution has a concentration of 5 mol/dm³ and a molar mass of 40 g/mol, what is the concentration of the solution in g/dm³?
If a solution has a concentration of 5 mol/dm³ and a molar mass of 40 g/mol, what is the concentration of the solution in g/dm³?
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Study Notes
The Mole
- A mole measures the amount of substance
- Equivalent to 6.022 × 10²³ particles (Avogadro's constant)
- Particles can be atoms, molecules, ions, or electrons
- Molar Mass (Mr): the relative formula mass (Mr) of a substance in grams is equal to 1 mole
- Units: grams per mole (g/mol)
- Formula: Moles = Mass (g) / Molar Mass (Mr)
Conservation of Mass
- Law of Conservation of Mass: the total mass of reactants equals the total mass of products in a chemical reaction.
- Closed Systems: No mass is lost or gained
- Open Systems: Apparent mass changes may occur due to gases entering or leaving
Reacting Mass Calculations
- Steps for reacting mass calculation:
- Write a balanced chemical equation
- Identify substances given and required
- Calculate moles of given substance
- Find moles of required using mole ratio from balanced equation
- Convert moles to mass of required substance using: Mass (g) = Moles × Molar Mass (Mr)
Limiting Reactants
- Limiting Reactant: The reactant completely used up in a reaction and determines how much product is formed.
- Excess reactants: Not completely consumed.
- Steps for identifying the limiting reactant:
- Calculate moles of each reactant.
- Use balanced equation to find the mole ratio.
- Identify which reactant is limiting (the one with fewer moles relative to the ratio).
Concentration of Solutions
- Concentration Formula: Concentration (mol/dm³) = Moles of solute (mol) / Volume of solution (dm³)
- Units: mol/dm³ or g/dm³
- Conversion between units: Concentration (g/dm³) = Concentration (mol/dm³) × Molar Mass (Mr)
Titrations
- Purpose: Determine unknown concentration of an acid or alkali by reacting with a solution of known concentration
- Key Formula: Moles of acid = Moles of alkali, C₁V₁ = C₂V₂
- Steps for titration:
- Measure a known volume of acid/alkali
- Add indicator (e.g., phenolphthalein or methyl orange)
- Slowly add the other solution from burette until indicator changes colour
- Record volume used and repeat for concordant results
Percentage Yield
- Definition: Compares actual mass of product obtained to maximum theoretical mass
- Formula: Percentage Yield = (Actual Yield / Theoretical Yield) × 100
Atom Economy
- Definition: Measures efficiency of a reaction based on how much of reactants become useful products.
- Formula: Atom Economy = (Mr of desired product / Total Mr of all products) × 100
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Description
This quiz covers essential concepts related to the mole, including its definition, Avogadro's constant, and molar mass calculations. Additionally, it explores the law of conservation of mass and the approach to reacting mass calculations, featuring limiting reactants as well. Test your understanding of these fundamental chemistry principles.
