Tonicity

Acids are chemical compounds that release hydrogen ions (H+) when placed in water. For example, when hydrogen chloride is placed in water, it releases its hydrogen ions and the solution becomes hydrochloric acid. Bases are chemical compounds that attract hydrogen atoms when they are placed in water.

Adding water to an acid or base will change its pH. Water is mostly water molecules so adding water to an acid or base reduces the concentration of ions in the solution. When an acidic solution is diluted with water the concentration of H + ions decreases and the pH of the solution increases towards 7.

acid

Week 1 A&P Chp2

As acid is added to a solution, the pH decreases. The pH at equivalence depends on the relative strengths of the acid and base in solution.

When the pH of a substance is above 7, it is a basic substance. When the pH of a substance is below 7, it is an acid substance. The further the pH lies above or below 7, the more basic or acid a solution is.

Generally, dilution has NO effect on the pH. Why is this so? If you look at the buffer formula, pH = pKa + lg [salt]/[acid], dilution does not affect the [salt]/[acid] ratio. i.e. they are diluted to the same extent or volume would cancel out.

The pH value of a solution directly measures the concentration of hydrogen ions (H+) in the solution. Acids have a large H+ concentration, which translates to a small pH value. Bases have very little H+. Basic solutions have large pH values – greater than pH 7.

pH is the negative base 10 logarithm (“log” on a calculator) of the hydrogen ion concentration of a solution. To calculate it, take the log of a given hydrogen ion concentration and reverse the sign.

A solution with a pH of 7 is classified as neutral. If the pH is lower than 7, the solution is acidic. When pH is higher than 7, the solution is basic. These numbers describe the concentration of hydrogen ions in the solution and increase on a negative logarithmic scale.

Each number represents a 10-fold change in the acidity/basicness of the water. Water with a pH of five is ten times more acidic than water having a pH of six. As this diagram shows, pH ranges from 0 to 14, with 7 being neutral. pHs less than 7 are acidic while pHs greater than 7 are alkaline (basic).

Your blood has a normal pH range of 7.35 to 7.45. This means that blood is naturally slightly alkaline or basic. In comparison, your stomach acid has a pH of around 1.5 to 3.5. This makes it acidic.

pH is usually (but not always) between 0 and 14. Knowing the dependence of pH on [H+], we can summarize as follows: If pH < 7, then the solution is acidic. If pH = 7, then the solution is neutral.

The scale has values ranging from zero (the most acidic) to 14 (the most basic). As you can see from the pH scale above, pure water has a pH value of 7. This value is considered neutral—neither acidic or basic. Normal, clean rain has a pH value of between 5.0 and 5.5, which is slightly acidic.

Question 2.

Barium hydroxide

Introduction to pH – acidic and basic (alkaline)

Solution : CH2-O∣∣C-CH2-O∣∣C-CH2-CH3,(-CH2-) group is flanked on both sides by electron-withdrawing groups and hence its hydrogen are most acidic.

Explanation: ‘acidic hydrogen means, it has tendency to be released as H+ ion . So, if any H-atom is attached to another atom or group of atoms with higher electronegativity, that H-atom is a potential acidic H-atom.

Ethyne

⟶CF3 has more negative Inductive effect than other group. Hence hydrogen attached to oxygen, experiences more negative Inductive effect and is more acidic.

Hence, we conclude that the hydrogen in Option (3) is the least acidic.

Therefore, HCOOH is weakest acid among the given choices.

There are 7 strong acids: chloric acid, hydrobromic acid, hydrochloric acid, hydroiodic acid, nitric acid, perchloric acid, and sulfuric acid. Being part of the list of strong acids doesn’t give any indication of how dangerous or damaging an acid is though.

Examples of Weak Acids

• Formic acid (chemical formula: HCOOH)
• Acetic acid (chemical formula: CH3COOH)
• Benzoic acid (chemical formula: C6H5COOH)
• Oxalic acid (chemical formula: C2H2O4)
• Hydrofluoric acid (chemical formula: HF)
• Nitrous acid (chemical formula: HNO2)
• Sulfurous acid (chemical formula: H2SO3)
• Phosphoric acid (chemical formula: H3PO4)

Weak Acids & Bases

It may be 1% ionized or 99% ionized, but it is still classified as a weak acid. The issue is similar with bases: a strong base is a base that is 100% ionized in solution. If it is less than 100% ionized in solution, it is a weak base….Learning Objectives.