Asample of white gold is: 18.0 grams gold, 3.0 grams silver, 2.0 grams cobalt, and 1.0 gram platinum by mass. what is the percent platinum in the sample?

The answer is: 4.16%

Explanation:

In order to know the percentage of one of the elements in the white gold, first we need to add all the components to know the total mass of gold we have. So, 18+3+2+1=24. The total mass of white gold is 24 g. Now, if 1 g of the total 24 g of gold is platinum, divide 1 g between 24 g and multiply by 100 to know the percent: (1/24) * 100 = 4.16 %

a c d and f

just finished the assignment

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol