Stoichemstry-PHAY0002 - 2

• What does the SI symbol 'n' represent in chemistry?

  Amount of substance (number of moles)
• What is the unit for the amount of substance?

  Mole (symbol mol)
• Why do we use the term 'entities' in chemistry?

  To include atoms, molecules, ions, and other particles
• How do you calculate the amount of sodium pertechnetate in moles from entities?

  $n =$$\frac{2.5 \times 10^{12}}{6.022 \times 10^{23}} =$$4.151 \times 10^{-12} \text{ mol}$
• What is the relationship between moles and entities?


  Entities refer to actual particles, while moles are a counting unit
• What is the formula for concentration?


  Concentration = quantity of substance / volume of solution
• What does molarity represent?


  Molarity is the amount of substance in moles per liter of solution
• What is the molarity of a solution with 1.7753 g of potassium iodate in 500.0 mL?


  $0.01659 \text{ M}$
• How do you calculate the amount of sodium in 10 mL of a 0.1 m sodium sulphate solution?


  $2.0 \times 10^{-3} \text{ mol}$
• What is the total amount of sodium chloride when mixing 25 mL of 0.30 m and 50 mL of 0.15 m solutions?


  $0.015 \text{ mol}$
• What is the concentration of the final solution after mixing the sodium chloride solutions?


  $0.2 \text{ M}$
• What is the glucose concentration in a 25 mL solution if 10 mmol of glucose is dissolved?


  $0.40 \text{ M}$
• How is percentage mass in mass calculated?


  Percentage mass in mass = (Mass of substance / Mass of sample) x 100
• What is the percentage of zinc oxide in a sample containing 0.3425 g of zinc oxide in 1.4326 g of paste?


  $23.9\%$
• How is percentage mass in volume calculated?


  Percentage mass in volume = (Mass of substance / Volume in solution) x 100
• What does the symbol % w/v represent?


  Grams of solute per 100 mL of solution
• What is the significance of mixing liquids in terms of volume?


  • Final volume is not equal to the sum of individual volumes
  • Volume in volume percentages should be used for approximate work
• What is the difference between ratios and parts in solutions?


  • Ratios indicate total volume (e.g., 1:5 means 1 mL of A and 5 mL of B)
  • Parts indicate specific volumes (e.g., 1 part in 5 means 1 mL of A in 5 mL total)
• What is stoichiometry in chemical reactions?


  Stoichiometry determines the ratio in which compounds react
• What is the balanced equation for the reaction between hydrochloric acid and sodium hydroxide?


  $1 \text{ HCl} +$$1 \text{ NaOH} \rightarrow 1 \text{ NaCl} +$$1 \text{ H2O}$
• What is the balanced equation for the reaction between phosphoric acid and sodium carbonate?


  $2 \text{ H3PO4} +$$3 \text{ Na2CO3} \rightarrow 2 \text{ Na3PO4} +$$3 \text{ CO2} +$$3 \text{ H2O}$
• What factors affect the efficiency of chemical reactions?

  • Reaction conditions (temperature, pressure, time, solvent)
  • Choice of reactants and reagents
  • Properties of starting materials
  • Activation energy
  • Stability of starting materials and products
• What does stoichiometry in chemical reactions refer to?


  It refers to determining the ratio in which two or more compounds react.
• What is the balanced equation for the reaction between hydrochloric acid and sodium hydroxide?


  1HCl + 1NaOH → 1NaCl + 1H2O
• What is the balanced equation for the reaction involving phosphoric acid and sodium carbonate?


  2H3PO4 + 3Na2CO3 → 2Na3PO4 + 3CO2 + 3H2O
• What factors affect the success of a chemical reaction?


  Factors include reaction conditions, choice of reactants, properties of starting materials, activation energy, stability, side reactions, and operator-related factors.
• What does stoichiometry tell us about a chemical reaction?


  It tells us how much product we should expect based on a given amount of starting material.
• How do we calculate the yield of a chemical reaction?

  Yield is calculated as the actual yield divided by the theoretical yield.
• What is the formula for yield in a chemical reaction?

  Yield = actual / theoretical
• Why is the yield typically less than 100%?


  Due to various factors affecting the reaction efficiency.
• What might a yield greater than 100% indicate?


  It may indicate contamination, the product is not dry, or weighing error.
• What does the conservation of matter imply about yield?


  It implies that the yield should not exceed 100%.
• How do you calculate the volume of a sphere representing a cell with a radius of 7.5 µm?


  Volume = $\frac{4}{3} \pi r^3 =$$\frac{4}{3} \pi (7.5 \times 10^{-6} m)^3 =$$1.8 \times 10^{-15} m^3$
• How do you calculate the number of moles from concentration and volume?


  Number of moles = concentration × volume.
• How do you calculate the number of molecules from moles?


  Number of molecules = number of moles × Avogadro's constant.
• What are the steps involved in multi-step drug synthesis?


  • Identify the limiting reagent for each step.
  • Calculate individual yields for each step.
  • Understand that convergent synthesis often results in higher overall yields.
• What is the difference between linear and convergent synthesis?


  Linear Synthesis:

  • Sequential steps.
  • Higher cumulative yield loss.

  
  

  Convergent Synthesis:

  • Parallel steps.
  • Lower cumulative yield loss.
• What is the overall yield for a linear synthesis with each step having an 80% yield?


  Only 32.7% of the starting material ends up as the final product.
• What is the overall yield for a convergent synthesis with each branch having an 80% yield?


  The final yield can be higher at 41%.
• Why is convergent synthesis more efficient than linear synthesis?


  Because it reduces the number of sequential steps, minimizing yield loss.