a normal penny has a mass of about 2.5g. if we assume the penny to be pure copper (which means the penny is very old since newer pennies are a mixture of copper and zinc), how many atoms of copper do 9 pennies contain?

Answer:

data given

mass of NaCl 4.56

dissolved volume 20ml(0.02l)

density of solution 1.03g/ml

Required molality

Explanation:

molarity=m/mr×v

where

m is mass

mr molar mass

v is volume

now,

molarity=4.56/58.5×0.02

molarity =3.9

: .molarity is 3.9mol/dm^3

According to molal concentration, the concentration (in molality) of an aqueous solution of NaCl is 0.0047 mole/kg.

Molal concentration is defined as a measure by which concentration of chemical substances present in a solution are determined. It is defined in particular reference to solute concentration in a solution . Most commonly used unit for molal concentration is moles/kg.

The molal concentration depends on change in volume of the solution which is mainly due to thermal expansion. Molal concentration is calculated by the formula, molal concentration=mass/ molar mass ×1/mass of solvent in kg.

In terms of moles, it's formula is given as molal concentration= number of moles /mass of solvent in kg.

Substitution in formula gives the answer but first mass of solution is determined which  is density×volume= 1.03×20=20.6 g , mass of solvent= 20.6-4.56=16.05, thus molal concentration=4.56/58.5×1/16.05=0.0047 moles/kg.

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Answer:

condensation nuclei

Explanation:

1) 5.1167 x 10²⁴atoms of chlorine. 2) 248.00 g. 3) 4.8825 x 10⁷ moles of helium. 4) 2.7757 x 10²⁴ atoms of sulfur.  5) Molar mass of Co (cobalt) is 58.93 g/mol.  6) Formula mass =  310.18 g/mol.

Sum of the atomic masses of all the atoms in chemical formula is called formula mass

1.)  Number of atoms = 8.500 moles x 6.022 x 10²³ atoms/mole = 5.1167 x 10²⁴ atoms of chlorine.

2.) Molar mass of oxygen is 16.00 g/mol. Therefore:

Mass of 15.50 moles of oxygen = 15.50 moles x 16.00 g/mol = 248.00 g.

3.) Molar mass of helium is 4.00 g/mol. Therefore, the number of moles of helium in 1.953 x 10⁸ g is:

Number of moles = 1.953 x 10⁸ g / 4.00 g/mol = 4.8825 x 10⁷ moles of helium.

4.) Molar mass of sulfur is 32.06 g/mol. Therefore, the number of moles of sulfur in 147.82 g is:

Number of moles = 147.82 g / 32.06 g/mol = 4.6084 moles of sulfur.

To find the number of atoms, we can use Avogadro's number again:

Number of atoms = 4.6084 moles x 6.022 x 10²³ atoms/mole = 2.7757 x 10²⁴ atoms of sulfur.

5.) Molar mass of Co (cobalt) is 58.93 g/mol.

6.) Ca₃(PO₄)₂ contains 3 calcium atoms, 2 phosphorus atoms, and 8 oxygen atoms.

Atomic masses of these elements are:

Calcium (Ca) = 40.08 g/mol

Phosphorus (P) = 30.97 g/mol

Oxygen (O) = 16.00 g/mol

Therefore, formula mass of Ca₃(PO₄)₂ is:

Formula mass = (3 x 40.08 g/mol) + (2 x 30.97 g/mol) + (8 x 16.00 g/mol)

= 120.24 g/mol + 61.94 g/mol + 128.00 g/mol

= 310.18 g/mol.

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