Chemistry Assessments Chem 16A

Chemistry Assessments

Chem 16A

• a) 2HCl(aq) + Mg(OH)₂(aq) → MgCl₂(aq) + 2H₂O(l)

b) Using 22ml of 0.7M HCl and 14.7ml of 0.55M Mg(OH)₂ the reaction would proceed as follows;

The mole ratio for the reactants is 2:1 for each mole of Mg(OH)₂, two moles of HCl are required. Thus, for 0.008085Moles of Mg(OH)₂ to be fully consumed, there must be 0.01617 moles of HCl. This is less than the 0.0154 moles provided making HCl the limiting reagent (Da Silva, 2017). Thus, the products formed will depend on the moles of HCl used.

The mole ration of HCl to MgCl₂ is 2:1. Therefore, two moles of HCl produce 1 mole of MgCl₂. Since 0.0154 moles of HCl were used, then of MgCl₂ were produced. Since the molar mass of MgCl2 is 95.211g/mol, it follows that the mass is

• a) H₂SO₄(aq) + Ca(OH)₂(aq) → CaSO₄(aq) + 2H₂O(l)

b) Using 36 ml of 0.2M H₂SO₄(aq) and 20 ml of 0.1M Ca(OH)₂(aq);

Since the mole ratio of the reactants is 1:1, then Ca(OH)₂ is the limiting reagents since it will be depleted first (Da Silva, 2017). It will therefore determine the moles of H₂O produced as follows;

In the last three balloons, some magnesium remains unconsumed, and it can be observed that the size of the balloons is comparatively similar. This is because all the HCl has been consumed, and there is none left to react with the remaining magnesium. This makes HCl the limiting reagent and Mg the excess reagent because HCl hindered Hydrogen production.

• Unbalanced Equation; Mg(s) + HCl(aq) →H₂(g) + MgCl₂(aq)

Balanced Equation; Mg(s) + 2HCl(aq) →H₂(g) + MgCl₂(aq)

From the video, it can be observed that 82mmol of HCl(aq) reacted with 41mmols of Magnesium in the balloon where the reactants were all consumed (Jim Holler, 2012). This makes it a 2:1 mole ratio used to balance the above equation.

Chem 17A

After;  NaOH → Na⁺ + OH^-

  0   100% or 1M

In contrast, ammonium hydroxide is a weak base that undergoes partial dissociation in water to form ammonium ions and hydroxyl ions. Represented in an equation, the dissociation will be as follows.

Before;  NH₄OH ⇌ NH₄⁺ + OH^-

  100% or 1M   0

After;  NH₄OH ⇌ NH₄⁺ + OH^-

   99% or 0.99M 1% or 0.01M

Conductivity and pH

 An increase in the concentration of ions in a solution is associated with an increase in conductivity (Atlas Scientific, 2022). As such, a solution with more free ions will have higher conductivity. In this case, sodium hydroxide has 1M free ions compared to ammonium hydroxide, which has 0.01M. It is expected that sodium will have a significantly higher conductivity.

 With regard to pH, pH is a measure of the relative amount of free hydrogen and hydroxyl ions, which means that water with more hydrogen or hydroxyl ions is more acidic or basic, respectively. In this case, sodium hydroxide has more free hydroxyl ions, 1M, than ammonium hydroxide, 0.01M. Its pH would be, therefore, higher, closer to 14, than ammonium hydroxide’s, which would be closer to 7.

Reactivity

 The dissolved oxygen decreases from point A, 8 ppm, to point B, 7 ppm, and more on point C, 3 ppm. The increase in Nitrates can explain this, and phosphates in the river are due to agricultural and livestock wastes from the pig farm. A minimum of 5 ppm of dissolved oxygen is required for aquatic life. The suspended solids are low in point A, high in point B, and medium in point C. This is associated with the acidity of the water that favors the accumulation of metallic waste from the metal stripping plant.

Thus, both the pig farm and metal stripping plant are contributing to fish death. The metal stripping plant acidifies water and releases metallic waste favoring their accumulation. This is toxic to the fish and leads to death. The pig farm releases phosphates and nitrates, reducing the dissolved oxygen, which deprives aquatic life of oxygen, leading to death.