Pure platinum is too soft to be used in jewelry because it scratches easily. to increase the hardness so that it can be used in jewelry, platinum is combined with other metals to form an alloy. to determine the amount of platinum in an alloy, a 7.518 g sample of an alloy containing platinum and cobalt is reacted with excess nitric acid to form 1.23 g of cobalt(ii) nitrate. calculate the mass percent of platinum in the alloy.

94.7%

Explanation:

The equation of the reaction:

Co(s) + 2HNO3(aq) > Co(NO3)2(aq) + H2(g)

Number of moles = mass of substance/ molar mass of cobalt II nitrate

Number of moles= 1.23g/182.943 g/mol = 6.7×10^-3 moles

From the reaction equation, 1 mole of Cobalt metal gave 1 mole of Cobalt II nitrate

x moles of Cobalt will give 6.7×10^-3 moles of Cobalt II nitrate

x= 6.7×10^-3 moles of Cobalt metal

Mass of cobalt metal = number of moles × molar mass

Molar mass of cobalt metal= 59gmol-1

Mass of cobalt= 6.7×10^-3 moles× 59gmol-1

Mass of cobalt= 0.40 g

Mass of platinum in the sample= 7.518-0.40= 7.118 g

% mass of platinum= 7.118/7.518 × 100

% mass of platinum= 94.7%

first let us lay out the formula for potential

and kinetic energy:

pe = mgh

ke = (mv^2)/2

where: m=mass, v=velocity, g=gravitational

acceleration, h=height

calculating for mass using the known values of

pe:

340j = m (9.81 m/s^2) (50ft) (1m/3.28ft)

m = 2.27 kg

the law of conservation of energy states that

energy is neither created nor destroyed. therefore, the change in kinetic

energy from 50 ft to 35 ft would be equal to the change in potential energy

from 50 ft to 35 ft. however it would be opposite in signs since one is losing

while other is gaining.

ke(35ft) – ke(50ft) = - [ pe(35ft) – pe(50ft]

ke(50ft) = 0 since the brick is initially at rest

ke(35ft) = 340j - 2.27kg (9.81 m/s^2) (35ft)

(1m/3.28 ft)

ke(35ft)

= 102.38 j

14,16 18 reacts with group