SC8d Alkalis and Balancing Equations Flashcards
what is a base?
any substance that reacts with an acid to form a salt and water only.
are many bases soluble or insoluble in water?
insoluble
example of insoluble bases?
metal oxide
what is a base that is soluble in water?
alkali
example of soluble base (alkali)
metal hydroxide
what do alkalis form?
alkaline solutions with pH values of above 7.
core practical for change in pH using calcium hydroxide and magnesium hydroxide - very long and painful to remember
A. Use a measuring cylinder to add 50cm3 of dilute hydrochloric acid to a beaker.
B. Estimate and record the pH of the contents of the beaker
~Put a piece of universal indicator paper onto a white tile.
~Dip the end of a glass rod into the liquid, then tap it onto the paper.
~Wait 30 seconds, then match the colour to the right pH on a pH colour chart.
~Rinse the glass rod with water.
C. Add the measured amount (0.3g) of Ca(OH)2 powder to the beaker and stir. Then estimate and record the pH.
D. Repeat steps B. and C. 7 times so that you’ve added a total of 2.4g of powder.
E. Plot a graph with pH on the vertical axis and mass of calcium hydroxide on the horizontal axis.
core practical for change in pH using calcium hydroxide and magnesium hydroxide
A. Use a measuring cylinder to add 50cm3 of dilute hydrochloric acid to a beaker.
B. Estimate and record the pH of the contents of the beaker
~Put a piece of universal indicator paper onto a white tile.
~Dip the end of a glass rod into the liquid, then tap it onto the paper.
~Wait 30 seconds, then match the colour to the right pH on a pH colour chart.
~Rinse the glass rod with water.
C. Add the measured amount (0.3g) of Ca(OH)2 powder to the beaker and stir. Then estimate and record the pH.
D. Repeat steps B. and C. 7 times so that you’ve added a total of 2.4g of powder.
E. Plot a graph with pH on the vertical axis and mass of calcium hydroxide on the horizontal axis.
what do metals in group 1 and 2 form?
metal hydroxides
formula for group 1 metal hydroxides
M = metals
MOH
e.g. LiOH
formula for metal hydroxides in group 2
M = metal
M(OH)₂
e.g. Ca(OH)₂
why is the formula for group 1 and 2 different.
this is because ions formed by group 1 ions have a +1 charge (e.g. Li+) so you need one of them to balance the charge on the OH-.
Group 2 ions have a 2+ charge (e.g. Ca2+) so you need 2 OH- ions to balance the 2+ charge.
what happens when an alkali is added to an acid?
pH increases
when does a acid neutralise
when the pH becomes 7
magnesium hydroxide reacts with stomach acid, which is hydrochloric acid. magnesium chloride solution is a product. write a balanced equation for the reaction, including state symbols. (3 marks)
Mg(OH)₂(aq) + 2HCl(aq) → MgCl₂(aq) + 2H₂O(l)
