<span>A chemical reactions :
Involves small amounts of energy.
</span><span> Only electrons are involved.
</span><span>The mass remains the same.</span>
For an aqueous solution of MgBr2, a freezing point depression occurs due to the rules of colligative properties. Since MgBr2 is an ionic compound, it acts a strong electrolyte; thus, dissociating completely in an aqueous solution. For the equation:
ΔTf<span> = (K</span>f)(<span>m)(i)
</span>where:
ΔTf = change in freezing point = (Ti - Tf)
Ti = freezing point of pure water = 0 celsius
Tf = freezing point of water with solute = ?
Kf = freezing point depression constant = 1.86 celsius-kg/mole (for water)
m = molality of solution (mol solute/kg solvent) = ?
i = ions in solution = 3
Computing for molality:
Molar mass of MgBr2 = 184.113 g/mol
m = 10.5g MgBr2 / 184.113/ 0.2 kg water = 0.285 mol/kg
For the problem,
ΔTf = (Kf)(m)(i) = 1.86(0.285)(3) = 1.59 = Ti - Tf = 0 - Tf
Tf = -1.59 celsius
Before proceeding, we should write the reaction equation to better understand what is happening:
2AgNO₃ + Na₂S → Ag₂S + 2NaNO₃
Now, we may apply the law of conservation of mass, due to which the total mass before a chemical reaction is equivalent to the total mass after a chemical reaction. Therefore:
Mass of silver nitrate + mass of sodium sulfide = mass of silver sulfide + mass of sodium nitrate
Mass of silver nitrate + 156.2 = 595.8 + 340
Mass of silver nitrate = 779.6 grams
Answer:
Percentage of copper = 88%
Explanation:
Given data:
Mass of copper = 51.2 g
Mass of tin = 6.84 g
Percentage of copper = ?
Solution:
Formula:
Percentage of copper = mass of copper / total mass × 100
Now we will determine the total mass:
Total mass = mass of copper + mass of tin
Total mass = 51.2 g + 6.84 g
Total mass = 58.04 g
Now we will calculate the percentage of copper.
Percentage of copper = 51.2 g / 58.04 g × 100
Percentage of copper = 0.88 × 100
Percentage of copper = 88%
