Correct answer: (2) 48.5 g

It is said that the 190.2-g sample only contains magnesium and chlorine. 74.5% by mass is accounted for as chlorine. Therefore, the magnesium component is at 25.5% by mass.

Answering the question:

The mass of magnesium can be calculated by getting 25.5% of the total weight of the sample. In this case, 25.5% of 190.2g is 48.5 g. Therefore, the answer for this question is option no. 2.

Options 1, 3 and 4 are eliminated.

Correct answer: (1) 20 ppm

The concentration of a solution is expressed as parts per million or ppm units.  It is the short version of metric units mg/L.  Therefore, it is known that 1 ppm is equivalent to 1 mg/L.

Answering the question:

We are given the masses of Na₃PO₄ as 0.02 g and H₂O as 1000 g.  The solubility expressed in ppm is actually the mass of the dissolved substance (Na₃PO₄) divided by the volume of the solvent (H₂O).  However, we can not directly proceed with the given data because we need to comply with mg/L unit to arrive with a concentration value in ppm.

First, the mass of Na₃PO₄ should be converted to mg unit.  0.02 g should be multiplied with the conversion factor of 1000 to arrive to the value of 20 mg.

Since we are only given 1000 g as the mass of water, we need to derive its volume in accordance to the given mass.

In order to get the volume, we will take the density of water at standard condition which is 1000 g/L.  Volume is then equal to mass of water divided by the density of water.  We will then arrive at the value of 1 L as the volume.

To get the concentration in ppm, we now divide the mass of Na₃PO₄ in mg unit with the volume of water in L unit.  This will give us the answer of 20 mg/L or 20 ppm which is option no. 1.

Therefore, options 2, 3 and 4 are all eliminated.

Correct Answer is six (6)

The above chemical equation shows the ratio needed for two reactants to completely form a product. Chemical equations like mathematical equations require balance. Therefore if we have 4 moles of an element as reactant we must be able to account for 4 moles of product. For example in the above equation 4 moles of Al_(s) is required, the à indicates that the 4Al_(s) is what is reacting to produce 2Al₂O₃. For Al this equation is balanced as 4Al à 2Al₂ therefore we can account for both the 4 moles of reactant and 4 moles of Al in the product. This must hold true for all elements in a chemical equation.

Answering the question:

Based on the above equation 4 moles of Al would be needed to react with 3 moles of O₂ in order for the reaction to go to completion resulting in 2 moles of Al₂O₃.

Using some basic math we can infer that 1 mole of Al would require four times less O₂ resulting in ¾ moles of O₂. Therefore 8 moles of Al would require eight times as much O₂ as 1 mole of Al which would be 8 x ¾ = 6. Therefore the new equation would read

8Al_(s) + 6O_2(g) → 4Al₂O_3(s)

Giving us an answer of 6

Correct Answer: 12 moles

Answering the questions:

Based on the above equation the number of electrons can be calculated for each element.

In the case of nickel it is Ni²⁺(aq) + 2e → Ni(s)

Therefore two moles of electrons are required for every mole of Ni²⁺ to be reduced. This is based on the fact that Ni²⁺ has a net positive charge as a result of having two more protons than electrons. That means 2 electrons would be required for every one Ni²⁺ to produce Ni(s). If 6 moles of Ni²⁺ are present then twice as many moles of electrons would be required.

Therefore the answer is 12

Correct Answer: 0.5 moles

Answering the Question:

The Cylinder contains 22g of CO₂. One molecule of CO₂ has a molecular mass of 12(mass of carbon) + 2x16 (mass of oxygen) = 44.

What that tells us is that 1 mole of CO₂ has a weight of 44g, as 1 mole of any substance is equal to the gram molecular weight of that substance. This means 1g of CO₂ has 1/44 moles.