Chemistry

The concentration (HI) is :- First calculate the moles (HI)

moles(HI) = 3g / ( 1 + 126.9)

moles(HI) = 3g/127.9 = 0.023455....

Since HI fully dissolves in water to

HI = H^(+) + I^(-)

Then by equivalence we have 0.023455... moles (H^(+) & 0.02345... ,Moles(I^(-)

This is contained in 500mL of water.

Hence the Conc'n is 0.023455...moles /0.500 L = 0.046911... M

As a definitive statement ' pH = the negative logarithm to the base ten of the hydrogen ion concentration.

Algebraically

pH = -log(10)[H^(+)]

Substituting

pH = -log(10)[0.046911....]

On your calculator , make sure you use the ;log; button, NOT the 'ln'. button.

pH = -(-1.32871....)

pH = 1.32871... )

pH = 1.33 (NB pH is quoted to 2 d.p.)

c

Whatever the substance you first calculate the moles using the equation.

moles = mass(g) /Mr ; The n dissolve in sufficient water , but LESS THAN 500 mL, otherwise you will have an incorrect concentration. Then make up the volume to 500 mL.

The 'Mr' is the Relative Molecular Mass . To find the 'Mr' you need copy of the Periodic Table , with the Atomic Masses displayed.

So using Common Salt ( Sodium Chloride (NaCl) as an example) . The Mr( Sodium Chloride) is

NaCl

1 x Na = 1 x 23 = 23

1 x Cl = 1 x 35.5 = 35.5

23 + 35.5 = 58.5 is the Mr (NaCl)

So ubstitute into the equation.

moles = mass(g) / Mr

is

0.25 = mass(g) / 58.5

Algebraically rearrange

mass(NaCl) = 0.25 X 58.5 = 14.625 gram

So measure out on the weigh scale 14.625 gram. (NaCl)

Dissolve this mass in say 100 mL de-ionised water.

When fully dissolved add sufficient de-ionised water to make up to a volume of 500 mL.

NB; Do NOT dissolve the full mass in exactly 500 mL of water, because then you will have more than 500 mL of volume, and an incorrect concentration.

NNB: If using a different substance , say copper sulphate (CuSO4) you will need to re-calculate the 'Mr' from the given Atomic masses on the Periodic Table.

A numerically low pH indicates ACIDITY.

NB

pH ; 0 - 6 is Acidic

pH ; 7 is neutral (Water)

pH 8 - 14 is Alkaline(basic)

NO!!!!

They are isotopes.

The definition of an isotope is that it has a 'Different number of Neutrons', thereby giving it different atomic mass.

Ions are atoms that have lost or gained electrons , and are now correctly named IONS , NOT atoms.

Many substances are water-sensitive, but one of the most notable is certain types of hygroscopic materials, such as anhydrous salts (like calcium chloride). These substances can absorb moisture from the air and may undergo physical or chemical changes when exposed to water. Other examples include certain pharmaceuticals, which can degrade in the presence of moisture. Additionally, some metals, like iron and aluminum, can be sensitive to water, leading to corrosion or rusting when exposed.

The standard Gibbs free energy change (ΔG°) in chemical reactions is significant because it determines whether a reaction is spontaneous or non-spontaneous under standard conditions (1 atm pressure, 298 K temperature, and 1 M concentration for all reactants and products).

If ΔG° < 0, the reaction is spontaneous, meaning it can proceed without external energy input.

If ΔG° > 0, the reaction is non-spontaneous, requiring external energy to proceed.

If ΔG° = 0, the system is at equilibrium, and no net reaction occurs.

This value is crucial for predicting the direction and feasibility of chemical reactions.

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Solids exhibit a greater force of intermolecular attraction compared to liquids and gases. In solids, particles are closely packed in a fixed arrangement, leading to strong interactions between them. In contrast, liquids have weaker intermolecular forces, allowing particles to slide past one another, while gases have the weakest intermolecular attractions, resulting in particles that are far apart and move freely.

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To find the pH from the hydroxide ion concentration (OH⁻), you can use the formula pOH = -log[OH⁻]. Given that [OH⁻] = 9.0 × 10⁻⁷ M, the pOH is approximately 6.05. Since pH + pOH = 14, the pH can be calculated as pH = 14 - pOH, which results in a pH of approximately 7.95.

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Of a given element they have the SAME number of PROTONS.

e.g.

Chlorine exists as the chloride ion ' Cl^(-)

Chlorine also exists as two isotopes ' Cl-35 & Cl-37 '

So you can have a chloride-35 ion ( 35-Cl^(-) ) and a chloride-37ion ( 37-Cl^(-)).

But of all these different characteristics of chlorine , they ALL have the SAME number of protons at 17.

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