PH值會唔會過負

Consider pH = - log[H+], pH is an indication of acidity and the concentration of H+ in the solutions.

Usually we hv very small H+ concentration in most chemicals and solutions e.g. 0.0001M of H+, using the above fomula, u will get pH=4.
In fact, there are situations when u can get a -ve pH. This is when you hv a very high H+ concentration in your solution. For instance, in 10M HCl, the [H+]will be 10M. Using the formula, pH = - log10 and u'll get pH = -1.
10M HCl usually not found in labs in secondary/high schools since it is very acidic and corrosive.

pH usually ranges form 1 to 14 because the chemicals we deal with are usually within this range. and this is why we hv pH papers that measure this range. If you want to measure a larger range , u can use a pH meter which gives more accurate results.

呢排唔得閒唔記得左choice人

而家變左投票sor~

Visual representation of the pH scale.
Another visual representation of the pH scale.In simpler terms, the number arises from a measure of the activity of hydrogen ions (or their equivalent) in the solution. The pH scale is an inverse logarithmic representation of hydrogen proton (H+) concentration. Unlike linear scales, which have a constant relationship between the item being measured (H+ concentration in this case) and the value reported, each individual pH unit is a factor of 10 different than the next higher or lower unit. For example, a change in pH from 2 to 3 represents a 10-fold decrease in H+ concentration, and a shift from 2 to 4 represents a one-hundred (10 × 10)-fold decrease in H+ concentration. The formula for calculating pH is:


Where αH+ denotes the activity of H+ ions, and is dimensionless. In solutions containing other ions, activity and concentration will not generally be the same. Activity is a measure of the effective concentration of hydrogen ions, rather than the actual concentration; it includes the fact that other ions surrounding hydrogen ions will shield them and affect their ability to participate in chemical reactions. These other ions change the effective amount of hydrogen ion concentration in any process that involves H+.

In dilute solutions (such as tap water), activity is approximately equal to the numeric value of the concentration of the H+ ion, denoted as [H+] (or more accurately written, [H3O+]), measured in moles per litre (also known as molarity). Therefore, it is often convenient to define pH as:


For both definitions, log10 denotes the base-10 logarithm, therefore pH defines a logarithmic scale of acidity. For example, if one makes a lemonade with a H+ concentration of 0.0050 moles per litre, its pH would be:

第一位人兄唔識野就少出聲啦
pH係可以負架

大把野係 負pH啦

pH = -log [H+]

當H+的濃度唔係小數的時侯,pH就負

p.s. 大量的superacid可以去到-20,甚至-40

2008-03-01 02:47:57 補充：
一樓扮晒野
唔識野就死開啦
anti-matter

1樓你真係笑死人

第一位回答ｇｅ仁兄。
我想講係有<1&>14lor...
pH值係計佢氫離子ge多少...
只係我地日常用唔著<1 or >14 ge物質...
如果我無記錯...
氟銻酸係pH-25 lor!

There must have substances that have pH value below 0 (-ve) and beyond 14.
pH value is only a value related to the concentration of H cation. The reason why we always say the pH value is within the range of 1-14 is that this is the range that can be tested by pH paper. Any value beyond this range can only be detected by more advance equiments.

正確地係沒有的

因爲很多chemicals 只分爲 alkali, acid or neutral
而最強的acid = PH 1
最強的alkali = PH 14

如果是負的，那應該列為anti-matter (不全在物體)