A 1.018 g sample pure platinum metal was reacted with HCl to form 1.778 g of a compound containing only platinum and chlorine. What is the percent by mass of platinum?

57.26 %

Explanation:

Step 1: Write the balanced equation

Pt + 2 HCl ⇒ PtCl₂ + H₂

Step 2: Calculate the mass of Pt in 1.778 g of PtCl₂

According to the law of conservation of the mass, all the mass of Pt in the reactants must be present in the products. Since PtCl₂ is the only product that contains Pt, the mass of Pt is 1.018 g

Step 3: Calculate the percent by mass of platinum in PtCl₂

We will use the following expression.

%Pt = mPt / mPtCl₂ × 100%

%Pt = 1.018 g / 1.778 g × 100% = 57.26 %

the answers are

c and c