Winger Pocock went over early on after a good team move and only Niamh Briggs' superb tackle stopped Danielle Waterman getting try No.2 soon after.
But that soon arrived as fly-half Katie McLean's fed Alphonsi on the crash before Merchant was on hand to pick up the loose ball and dive over.
Ireland did enjoy plenty of possession but they could not break a resolute English defence.
And when the hosts turned defence into attack they were an irrestible force as Turner and the excellent Alphonsi added further scores.
Meanwhile Wales and Scotland face an uphill struggle to qualify for the knockout stages after losing to Australia and Canada respectively.
Wales were left to pay the price for a sluggish start after conceding three first-half tries in their 26-12 defeat as Ashley Beck, Sharni Williams and Cobie-Jane Morgan all crossed.
After the break Wales were much improved winning a penalty try before prop Lowri Harries also crashed over but Tricia Brown's score ensure Australia finished with a bonus point.
Scotland too were outclassed in the first 40 minutes of their 37-10 defeat to Canada.
Canada were 25-0 ahead at the break and even Lucy Millard and Lindsay Wheeler's second-half tries for the Scots could not salvage anything from the match.