MOLES & MOLAR MASS
Calculate the number of moles in 12.5 g of sodium carbonate .
0.118 moles
A compound contains 40% sulfur and 60% oxygen by mass. Calculate the empirical formula.
SO₃
Balance the following chemical equation:
C₃H₈ + O₂ --> CO₂ + H₂0
C₃H₈ + 5O₂ --> 3CO₂ + 4H₂0
What is the purpose of using a phenolphthalein indicator in an acid-base titration?
To determine the endpoint by changing color when the solution transitions from acidic to basic (colorless in acid to pink in base
What is the primary purpose of using a control experiment in practical chemistry?
To provide a baseline for comparison, ensuring that the observed effect is due to the variable being tested.
if 4.4 g of carbon dioxide is produced in a reaction , how many molecules of CO2 are formed ?
6.02x10²² molecules
A compound has an empirical formula of CH₂O and a molar mass of 180 g/mol. What is the molecular formula of the compound?
C₆H₁₂O₆
Write the balanced chemical equation for the complete combustion of ethanol
C₂H₅OH + 3O₂ --> 2CO₂ + 3H₂0
In a titration, 25.0 cm³ of 0.1 M hydrochloric acid (HCl) is neutralized by 20.0 cm³ of sodium hydroxide (NaOH). What is the concentration of the NaOH solution?
0.125 M
When measuring the volume of a liquid using a burette, why is it important to remove the air bubble from the tip before starting the titration?
To ensure accurate volume measurement and avoid errors caused by air pockets.
Calculate the mass of oxygen gas required to completely react with 0.5 moles of ethane in the following reaction :
2C2H6+7O2→4CO2+6H2O
112 g
Determine the empirical formula of a compound that contains 92.3% carbon and 7.7% hydrogen by mass.
CH
A 10 g sample of calcium carbonate (CaCO₃) decomposes upon heating according to the following reaction:
CaCO3(s)→CaO(s)+CO2(g)
Calculate the mass of calcium oxide (CaO) produced.
5.6 g
A titration experiment requires 24.5 cm³ of 0.1 M NaOH to neutralize 25.0 cm³ of sulfuric acid (H₂SO₄). Calculate the concentration of the sulfuric acid.
0.049 M
Explain why it is important to rinse the inside of a conical flask with distilled water during a titration but not with the titrant.
Rinsing with distilled water does not affect the concentration of the solution in the flask, ensuring that only the titrant reacts with the analyte.
A sample of hydrated copper(II) sulfate, CuSO₄∙xH₂O, weighs 6.25 g. After heating, 4.00 g of anhydrous CuSO₄ remains. Determine the value of x
x = 5
A compound contains 27.3% carbon, 72.7% oxygen by mass, and has a molar mass of 88 g/mol. Determine the molecular formula.
C₂O₄
Balance the following redox reaction in acidic solution
MnO4⁻ + Fe2⁺ → Mn2⁺ + Fe3⁺
MnO4⁻ + 5Fe2⁺ +8H⁺→Mn2⁺+5Fe3⁺ + 4H2O
Calculate the percentage purity of a sample of sodium carbonate (Na₂CO₃) if 1.06 g of the sample requires 25.0 cm³ of 0.1 M hydrochloric acid (HCl) for complete neutralization.
50%
In a reaction to determine the concentration of an unknown solution using a standard solution, why is it crucial to perform multiple titrations and calculate an average volume used?
To increase the accuracy and reliability of the results by minimizing random errors and ensuring that any anomalies or inconsistencies in individual titrations do not skew the final concentration calculation.
Calculate the empirical formula of a hydrocarbon that is 85.7% carbon and 14.3% hydrogen by mass.
C₇H₁₆
A hydrocarbon contains 80% carbon and 20% hydrogen by mass. If the molar mass of the compound is 30 g/mol, calculate the molecular formula.
C₂H₆
Given the reaction:
2Na2O2 + 2H2O → 4NaOH + O2
Calculate the volume of oxygen gas produced at room temperature and pressure (RTP) when 10 g of sodium peroxide (Na₂O₂) reacts completely with water.
1.54 dm³
During a titration, 0.5 g of impure oxalic acid (H₂C₂O₄) was titrated with 0.1 M NaOH. The titration required 25.0 cm³ of NaOH to reach the endpoint. Calculate the percentage purity of the oxalic acid.
55.6%
In a qualitative analysis, why is it important to add reagents in a specific order when testing for multiple ions in a single solution?
To prevent the formation of precipitates that could obscure the results, as adding reagents in the wrong order could cause interfering reactions or mask the presence of certain ions.