A five month old on average should be sleeping at least 10 hours (more closer to 12 hours though) a night, with perhaps a one or two hour nap during the day.
That depends on the schedule and whether or not the child is eating cereal or food yet. A bottle or formula only baby may only sleep 4 or 5 hours at one time where a cereal eating baby will likely sleep up to 6 or 8 hours per night with naps in the day.
Generally babies like sleeping most of the time but a 5 months old should sleep minimum 10 hours a day. Baby should sleep in a comfortable place for sound sleep.
Generally babies at that age sleep anywhere from two to four hours at a time, depending on their feeding schedule and diaper changes. Some may sleep shorter or longer, it all depends on the child.
